Growth-rings in the Cell Wall of Cotton Hairs. 



555 



DESCRIPTION OF PLATES. 



(All figures represent hairs of tlie author's No. 77 Pure Strain of Egyptian Cotton. 

 Acetic-absolute pickle, five years old.) 



Plate 14. 



Fig. 1. — Lint-hairs swollen to varying extents under nominally uniform treatment by 



CSj and NaOH. A cuticle girdle clearly shown, indicating original diameter 



of swollen hair, x 540. 

 Pig. 2. — Fuzz-hairs on 21st day of development of fruit (boll). Primary wall scarcely 



swollen by treatment, wrinkled and flaccid as in all preceding 20 days. 



X 360. 



Plate 15. 



Fig. 3. — Fuzz-hairs on 27th day, secondary thickening of wall having begun about 

 26th day. Two hairs well swollen, with only one growth-ring visible ; demar- 

 cation of secondary deposit from primary wall is indicated, x 360. 



Vig. 4. — Fuzz-hairs on 33rd day. Fine example of a wide girdle of cuticle ; also faint 

 spiral of same. Nine and ten growth-rings ; constriction in girdle clearly 

 shown. Swelling of cell-diameter is about three-fold, of wall is about seven- 

 fold. X 360. 



Fig. 5. — Fuzz-hairs on 36th day. Cuticular remains very evident as spirals. Firmness 

 of growth-layers in the jelly under bending stresses can be seen at corners 

 of photograph. 



Central hair happens to have same number of growth-rings as one in 

 fig. 4 ; the great difi'erence in appearance is thus merely due to the greater 

 swelling, which has magnified the cell-wall at least fifteen-fold. Magnifica- 

 tion of growth-rings in this photograph is thus 15 x 360 = 5000 about. 



Plate 16. 



Figs. 6 and 7. — Lint-hairs of 33rd day (for fuzz see fig. 4). Two successive photographs 

 with minute alteration of focus ; original focussing effected directly on surface 

 of a plate, not on groimd glass. The two hairs practically unaffected by 

 reagents indicate original dimensions of cell-wall. The swollen hair girdled 

 by cuticular spirals passed into complete solution a little way outside the 

 field of view ; maximum swelling in the field is about seventeen times the 

 wall thickness. It is difficult to photograph the hyaline layers satisfactorily 

 in optical section, but in various places the ten rings are indicated as a series 

 of shadings, x 540. 

 Maximum magnification of growth-rings here is 17 x .540 = 9000 about. 



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