This chapter reports the major findings, provides implications for vocabularyand writing teaching, points out the limitations and offers some suggestions forfuture research. 5.1 Major Findings This study investigates the influence of vocabulary knowledge and use of lexisin writing on writing quality. Summarizing the answers to the research questions, wehave obtained the following conclusions. 1. Generally speaking, the subjects total vocabulary knowledge, including receptive, productive and depth of vocabulary knowledge highly correlates with proficiency levels. High proficiency group performed significantly better than lower proficiency group on the total vocabulary knowledge. However, in the case of vocabulary size, there still exists a wide gap between the receptive and productive vocabulary size. Such a gap exists not only between the subjects of different proficiency levels but also within the same proficiency level. Although depth of vocabulary knowledge enjoys more importance than vocabulary size does, judging from the survey, it appears that the subjects development of depth of vocabulary is poorer than that of vocabulary size. 2. It is generally acknowledged that vocabulary size is an index of ones language proficiency, but the present study indicates that receptive vocabulary size doesnt correlate with writing proficiency. Receptive vocabulary size doesnt have direct influence on writing score, and learners with larger receptive vocabulary size dont necessarily score high in writing. Depth of vocabulary knowledge displays substantial correlations with writing quality (r=.621**). Productive vocabularyknowledge is significantly correlated with writing quality (r=.586**). In contrast,receptive vocabulary shows an indirect influence on writing quality by affecting lexical richness and text length of the writing. Therefore, depth of vocabulary knowledge arid productive vocabulary use play a very important role in writing quality. 3. The use of lexis in writing measured by lexical variation and lexical sophistication correlates significantly with writing quality, because the use of lexis in the subjects compositions can really reflect their productivity. Positive and moderate correlation is found between lexical variation and writing quality The use of the most frequent 1000 words enjoy a high and negative correlation with writing quality, and the use of the second most frequent 1,000 words and the words of beyond the most frequent 2,000 words enjoys a moderately high anal positive correlation with writing quality. The result indicates that a better piece of writing is featured by greater diversity of lexical choiceaand more use of relatively sophisticated words. However, most subjects among different proficiency groups tend to make more use of the most frequent 1000 words and less use of the second most frequent 1000 words and beyond 2000 words. 5.2 Implications The present study also provides insights into the teaching of vocabulary and writing as well as the acquisition of ESL vocabulary for English learners in China. Firstly, more importance should be assigned to high-frequency vocabulary. The high-frequency category in English consists of 2000 word families, which form the foundation of the vocabulary knowledge that all proficient users of the language must acquire. The high-frequency words are very important because these words cover a very large proportion of the running words in spoken and written texts and occur in all kinds of uses of the language. Therefore, considerable time and attention should be spent on these high-frequency words by teachers and students. Better method should be explicit teaching and explicit learning for high-frequency vocabulary.Schimitt (2000) mentions that the most frequent 2,000 words as the most commonly cited initial goal for beginners and agrees that these have to be taught explicitly. Meam(1996) claims that these are so essential for any real language use that it might be a good idea to teach them right at the beginning of the language course. Explicit vocabulary instruction is indispensable for vocabulary learning, but it is very important to make the learners responsible for their individual vocabulary leaming. According to Ellis, explicit learning is a snore conscious operation where the individual makes and tests hypotheses in a search for structure (Ellis, 1994: 214).Explicit learning can involve a search for rules, or applying given rules. It is strongly affected by the quality of the mental processing. What Ellis calls the "mediational" aspect is the linking of knowledge of the word form to knowledge of the meaning. What this means is that, especially for high-frequency words, teachers should explain the meaning of words, and learners should do exercises, look them up in dictionaries,and think out meanings. After brief attention to spelling and pronunciation, experience in meeting and producing the word form should be left to encounters inmeaning-focused use. Secondly, more attention should be paid to the productive vocabulary knowledge, since the results have shown that the productive mastery of vocabulary knowledge is far from satisfactory for subjects at different proficiency levels. There seem to be two important factors affecting productive vocabulary use: knowledge and motivation(Nation, 2001: 182) Productive vocabulary knowledge is closely related with depth of vocabulary knowledge. Productive knowledge of a word includes receptive knowledge and extends it. It involves knowing how to pronounce and write the word, how to use it in correct grammatical patterns along with the words it usually collocates with. Productive knowledge also involves not using the word too often if it is typically a low-frequency word, and using it in suitable situations. It involves using the word to stand for the meaning it represents and being able to think of suitable substitutes for the word if there are any. Thus, productive knowledge of vocabulary requires more learning than receptive knowledge Therefore,more time and repeated effort is needed to learn vocabulary for speaking and writing than is needed for listening and reading. On the other hand, motivation plays an important part in productive vocabulary use. Motivation here refers to the desire and opportunity to use a word. Although some vocabulary may be well known and could be used productively, it is not used and remains in the learners passive vocabulary and becomes part of `unmotivated vocabulary, because the opportunity and wish to use the particular word does not arise. Therefore, teachers should create more opportunities for EFL learners to activate these passive words and produce more vocabulary, and learners themselves should try to grasp as many opportunities as possible to increase their productivity. Thirdly, special courses about vocabulary should be designed to enhance students acquisition of depth of vocabulary knowledge instead of simply enlarging their vocabulary size. Teachers should stress the links among various types of vocabulary knowledge, and it will facilitate the formation of an effective semantic network in their mental lexicon. Once the semantic network is formed, the receptive and productive acquisition of vocabulary knowledge will be more developed. Lastly, as Ferris (1994) stated, ESL composition teaching typically focused on global organizational or rhetorical patterns and/or on specific mechanical errors (grammar, spelling, punctuation) that students make. This study indicates that students variation and sophistication in lexical use plays an important part in a piece of writing, too. So, teachers are hereby suggested to devote more attention to such two aspects of lexis in students writing through some activities in teaching writing. They can examine the choices utilized by successful and novice writers though in-class analysis of model essays. They can also do micro level work on individual student papers through teacher-student conferences, teacher commentary, or peer or self-evaluation. 5.3 Limitations of the Present Study Like all empirical studies, this study suffered from some limitations though it was designed carefully. First, the LFP measure adopted in the present study doesnt take error into account. It reveals nothing about how appropriately the words were used by the L2 writers. Word choice errors, however, are an aspect of L2 writing that appears to affect essay evaluations, even more than grammatical errors (Santos, 1988). So, future research should explore more about the accuracy of word use. Second, the subjects chosen for this study are from two grades of one university, so this may not be the ideal representative of the real distinction among different proficiency levels. 5.4 Suggestions for Future Research In consideration of the conclusions and limitations in this study, the following suggestions are proposed for future research. First, the future investigation can involve a larger sample of learners with different specialties and at different grades, for the sake of a deeper understanding about the relationship between vocabulary knowledge and writing quality. Second, the vocabulary chosen by student writers was found to vary significantly with topic type (Reid, 1990). However, the present study collected only one composition for each subject. So, future studies can examine the difference in word choice and use in writing under different types of topics. Finally, the tasks used in the study were all written. In the future studies, the UP measure could also be used to analyze spoken language. It might be interesting to compare lexical richness of spoken and written language samples of the same learners.