PHYSIOLOGY OF THE COTTON PLANT 29 



nucellus, it bores through the tissues of the latter, and 

 after literally squeezing its way through the firmer wall 

 of the megaspore, the end of the tube swells up and bursts. 

 From the torn end escape the two male gametes, one of 

 which passes to and fuses with the egg-cell, forming a 

 zygote, and thus beginning a new life-history. The other 

 male nucleus fuses with the two polar -nuclei, and the 

 triple nucleus thus formed serves later to provide the 

 endosperm. 



"The process is exceptionally rapid. Fertilization is 

 normally completed within thirty hours after the first 

 opening of the flower, i. e., by the afternoon of the follow- 

 ing day." 



32. The embryo. A period ranging from 40 to 60 

 days elapses from the time the cotton flower opens until 

 the mature boll is formed. During this time the embryo 

 is slowly developing inside the fertilized ovule, or seed. 

 When the embryo is one week old it has been found to 

 be just visible to the naked eye. It is somewhat heart- 

 shaped in general outline. The pointed end develops 

 into the radicle, or first root, while the two lobes go to 

 form the first leaves of the embryo. These first leaves 

 (cotyledons) are broader than the seed in which they are 

 contained, and hence are much folded within the seed coat. 

 It is in these first miniature leaves or cotyledons that 

 the oil content of the cotton seed is contained. 



