Growth-nngs in the Cell Wall of Cotton Hairs. 



551 



than the previous one as regards the lint, and seven hairs showed 10, 12, 13, 

 13, 13, 14, and 14 rings respectively. Subtracting the mean value, 13 rings, 

 from 39 days, brings us back correctly to the 26th day as the one on which 

 the first ring was formed. 



Forty-two-day Fruit. — In this preparation the mean apparent number of 

 fuzz-rings was again unchanged (7 '2), though one very definite example of 

 14 rings was noted. No countable lint rings were found. 



Mature, or Fifty -day Fruit. — The ripe fuzz and lint were examined in the 

 pickled material, but also in various samples of lint and of seed, both of this 

 No. 77 strain, and of others grown in Egypt and the Sudan. Less regular 

 rings were found in some American Upland and Indian lints. The counts of 

 rings in the lint could never be proved to exceed 25 in number, and the 

 smallest figure obtained with certainty was 20, these numbers agreeing 

 completely with expectation. Not more than 16 obvious rings have 

 yet been seen in the adult fuzz, but it was presently found that 

 the very decided line of demarcation, which the older growth-rings of the 

 fuzz display, is prone to become less definite in the later, innermost rings. 

 Further search showed that in some cases this decrease in definition was 

 progressive after the first three or four rings, while in others it was quite 

 sudden, and occasionally it was possible, in lucky preparations, to see clearly 

 that the innermost "ring" — as casual observation had judged it to be — was 

 actually compound (fig. 5 shows traces) and actually consisted of seven or 

 even more rings which were indistinguishable from those shown by the lint. 



This accounts for the apparent de^dation of the number of rings in the 

 fuzz from expectation based on our hypothesis. It does not exclude the 

 possibility, in all the other cases where the evidence was negative, that the 

 fuzz ceases to thicken its wall at an earlier date than does the lint, but 

 the trend of the facts is evidently opposed to the latter assumption, and it is 

 more reasonable to assume that the growth of secondary thickening in the 

 fuzz is less " inhibited " at first than in the lint. The converse inhibition 

 would seem to obtain as regards growth in length. 



It is a striking fact, well in line with all the data from genetics and from 

 the ordinary cytology of development, that the fuzz-hairs should degrade to 

 the production of walls resembling those of the lint-hairs, when they are in a 

 senescent condition,* and not before. The problems of cell-senescence in the 

 CQtton plant would seem to provide a most promising field for research. 



* "Temperature and Growth," 'Ann. Bot.,' p. 557 (1908) ; ' Eaw Cotton," pp. 44, 96, 

 99, etc. 



