68 THE DEVELOPMENT OF KAW COTTON 



26 millimetres i.e., 24 to 28 is attained by the twenty- 

 fifth day. Henceforward there is no visible change in 

 the external appearance of the boll until it begins to 

 show signs of cracking along the two or three lines of 

 dehiscence on the forty-fifth day. On the forty-eighth 

 day it is opening and hardening, and on the fiftieth day 

 is ready to pick. 



DEVELOPMENT OF THE SEED (Fig. 13). The ovule, 

 when fully matured and ready for fertilization, is about 

 1 millimetre long. After fertilization, when it receives 

 the designation of a seed, it increases at the following 

 rates : 



Third day . . 

 Sixth day . . 

 Ninth day. . 

 Twelfth day 

 Fifteenth day 

 Eighteenth day 



Length in Width in 



Millimetres. Millimetres. 



2 



31 



5 



6* 



Thenceforward the growth ceases rapidly, and 10 by 

 6 millimetres is the average size of the full-grown ripe 

 seed. 



THE ENDOSPERM (Fig. 11, A, k). The embryo sac of 

 the ripe ovule extends over about half its length. It main- 

 tains this proportionate size as the seed begins to enlarge, 

 and then encroaches on the neighbouring tissue. The 

 triple fusion nucleus already mentioned does not delay its 

 division like the egg, but by the evening of the da^ on 

 which fertilization took place (the first day of develop- 

 ment) has divided into two separate nuclei. These re- 

 peatedly divide, until by the third day there are some 

 hundreds of nuclei arranged in a layer of protoplasm 



