HAIRS. 



179 



D 



D 



ened with water (or better still in a fresh state), they are dis- 

 tinctly blue. 4. The protein layer, the cells of which contain 

 granular albuminoid matters. 



The layers just described are different in different seeds, and 

 sometimes different in 

 different parts of the 

 same seed-coat, so that 

 the division has really 

 little utilit3 T . 



505. The external in- 

 tegument or testa may 

 have well-developed hairs, 

 as has been shown in Vol- 

 ume I. p. 306. Only one 

 of these cases of hairs 

 can be here described ; 

 namely, those which form 

 the felted covering of cot- 

 ton-seeds, and which are 

 the "cotton" of commerce. These are slender cells with col- 

 lapsed walls. As they ap- 

 proach maturity, the cells 

 become more or less twisted ; 

 the resulting spiral is that 

 which imparts to cotton its 

 value as a material for spin- 

 ning. Some other seeds, 

 notably those of species of 

 Asclepias, have long and 

 strong hairs, but none of 

 these have any spiral twist 

 which fits them for textile 

 purposes. 



Regarding the size of cot- 

 ton "fibres' (hairs of the 

 seed) , the following meas- 

 urements by Ordway are of interest : Maximum length in the 

 " sea-island' 1 variety, about two inches (five centimeters); in 



FIG. 136. Cross-sections of cotton-fibres. A A, unmature fibres; B B, half-mature 

 fibres ; C C, fully mature fibres ; Z>, section of fibre, showing laminated cell-walls. 

 (Bowman.) 



FIG. 137. A, Glassy, structureless fibre; B, thin, pellucid, immature fibre; C, half 

 mature fibre, with thin cell-wall; D and E, fully mature fibre, with full twist and well- 

 defined cell-wall. (Bowman.) 



