STRUCTURE OF THE BOLL 71 



elongation in a radial direction, and their nuclei show up 

 very distinctly, scattered about all parts of the "palisade" 

 layer which is formed by this elongation. 



By the eighteenth day the nuclei of the " palisade " 

 layer have taken up their position at the outward end of 

 each palisade cell. 



By the twenty-first day the inner end of the palisade 

 cells has begun to thicken its walls, so that this layer, 

 when viewed in section, consists of one-half thick-walled, 

 clear, translucent, stony tissue, streaked by the original 

 cell walls, and the outer half of the zone alone contains 

 the nuclei and granular protoplasm, with the same walls 

 still relatively thin. 



The epidermis continues to increase the depth of its 

 constituent cells for another week, and the palisade layer 

 builds more and more thick cell wall on the inner end of 

 each of its own cells, thereby forcing its nuclei farther 

 and farther from the centre of the seed, so that some 

 three-quarters of the palisade zone consists of translucent 

 stony cell walls. 



About the twenty-seventh day, when the seed-coats 

 have reached the state of development described, a 

 marked chemical change takes place in the pigment 

 layers, which has not yet been investigated, but which 

 is of considerable interest because it denotes the be- 

 ginning of the second stage of boll maturation, during 

 which the lint is given its strength. The change shows 

 up in material which has been preserved in a mixture of 

 acetic acid and alcohol. All the bolls from the first stage 

 " pickle " to a green colour, which, of course, fades to 



