GOSSYPIUM 441 



somes for cultivated species of cotton is 16; but Skovsted (30, 31) 

 has reported several species with a haploid number of 13 chromo- 

 somes, as well as a triploid hybrid in Asiatic cotton with a somatic 

 chromosome count of 39, and tetraploids with 5x. 



Development of the Ovule. — The primordia of the ovules 

 arise on the placentae as rounded masses of meristematic cells at 

 about the time that the locules become closed. During the devel- 

 opment of the nucellus, a basal fold appears growing upward to 

 form the inner integument; and as the apex of the nucellus begins 

 to curve, a second fold initiates the outer integument, which soon 

 overgrows the inner one. Both continue their growth until they 

 completely cover the nucellus, except for a small micropylar open- 

 ing around which the outer integument forms a lip-like ring. The 

 inner integument is 10 to 11. layers in thickness at the time of flower- 

 ing, and the outer one from six to eight layers. While the integu- 

 ments develop, the ovule continues its curving growth until it 

 becomes completely anatropous; and as the ovule assumes this 

 position, the portion of the funiculus which is undiverged from 

 the integument elongates greatly, forming the raphe. (Fig. 1.16, 

 B-D.') 



Megasporogenesis and the Megagametophyte. — The early 

 development of the archesporial cell is similar to that found in most 

 dicotyledons. According to Gore (17), 



"it has its origin from a subepidermal cell of the nucellus and arises 

 before the differentiation of the integuments. From its division a 

 primary parietal cell and a primary sporogenous cell are formed. . . . 

 While this sporogenous cell increases in size and becomes the megaspore 

 mother cell, the primary parietal cell divides many times. The other 

 cells of the nucellus also divide periclinally and anticlinally, thus 

 embedding the megaspore mother cell in several layers of nucellar 

 tissue. The mature megaspore mother cell is somewhat elongated 

 and lies quite near the chalazal end." 



Reduction divisions result in the formation of a linear tetrad of 

 megaspores at the micropylar end of the ovule. The chalazal 

 megaspore functions; and the outer three abort, although Balls (3) 

 does report an anomalous condition in which the outermost or 

 micropylar megaspore may function. In the development of the 

 megagametophyte, three successive nuclear divisions result in an 

 eight-nucleate stage, and it becomes an elongated narrow structure 

 which extends close to the chalaza. (Fig. xi6, D.) Just prior to 



