ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



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described previously ; but the writer draws especial attention to the facts 

 that (1) they are present only in a small definite number of Composite 

 genera ; and (2) they are connected inti- 

 mately with the latex- tissue. This study is 

 based upon the isobilateral cauline leaves of 

 Lactuca saligna Linn., which bear cutinized 

 hairs as well as those of the type in question. 

 After a brief account of the internal leaf- 

 structure, in which he describes the close 

 relation between the latex-system and the 

 wood-vessels, the author proceeds to describe 

 the latex-hair as consisting usually of three 

 ceUs, derived from an epidermal cell. Of 

 these three, one much exceeds the other two 

 in size. These cells are in such close con- 

 nexion with the primary internal latex-tissue 

 that the wall between hair-cell and latex- 

 cell often breaks down. The author sug- 

 gests from these observations that the hairs 



in question are actually latex-secreting hairs ; and he emphasizes the 

 consequent continuity of these with the xylem itself. H. F. W. 



The Existence of Daily Growth-rings in the Cell -wall of Cotton 

 Hairs. — W. Lawrence-Balls {Proc. Roij. Soc, 1919, 90, Series B, 

 542-55). The present communication describes the structure of the 

 cellulose wall of the cotton hair, in relation to its development, as a con- 

 tinuation of observations previously published in " The Development 

 and Properties of Raw Cotton" (1915). Swelling the cellulose wall 



Tip of treated fuzzy hair showing details of growth-rings. The 

 two outermost rings broken away over actual tip ; the isolated 

 portion of the tenth ring could not be seen to be in connexion 

 with the main bulk of the ring. 



(treatment with CS.2 and NaOH) to some five or ten times its initial 

 thickness renders concentric layering visible. Material of known age 

 and development, fixed in Egypt, was examined by this method, and it 

 was found that there is only one thin primary layer while the hair is 

 growing in length, but that as soon as thickening of the wall sets in the 

 number of layers increases day by day up to a maximum of twenty-five, 

 when thickening is complete. As growth is arrested by sunshine in the 



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