546 THE STRUCTURE OF ECONOMIC PLANTS 



may happen during the early stages, or following the formation 

 of the eight-nucleate gametophyte. In commenting upon these 

 occurrences, Rees-Leonard states, 



"These irregularities which occur during macrosporogenesis and 

 the development and maturation of the macrogametophyte may 

 partially account for the failure of seed and fruit development in the 

 potato. There seems to be some correlation, however, between the 

 irregularities occurring during microsporogenesis and the development 

 of the pollen grains on the one hand, and those taking place during 

 macrosporogenesis and macrogametophyte development in the ovules 

 of the same flower on the other hand." 



Megasporogenesis and the Megagametophyte. — The forma- 

 tion of the partially campylotropous ovules from the massive 

 cauline placenta has been described in connection with the develop- 

 ment and structure of the seed. At the time that the ovules first 

 become slightly inclined the archesporial cell differentiates in the 

 hypodermis just over the bent tip of the ovule; and, according to 

 Bhaduri (5), this occurs prior to the differentiation of the integu- 

 ment. The archesporial cell, which is larger than the adjacent 

 cells of the hypodermis, functions directly as a megaspore mother 

 cell. It enlarges and becomes somewhat vacuolate prior to the 

 two successive divisions which result in the formation of a linear 

 tetrad of megaspores, each of which is invested with a distinct 

 cell wall. When first formed, the megaspores are alike in size 

 and content; but soon the one at the chalazal end of the nucellus 

 begins to enlarge and there is a gradual degeneration of the other 

 three, beginning at the micropylar end. The three disintegrated 

 megaspores form a cap over the functional one which by its growth 

 compresses the others into a compact mass. 



In the development of the megagametophyte from the functional 

 megaspore, the two-, four-, and eight-nucleate stages occur in 

 rapid succession. The synergids and megagamete are located 

 toward the micropyle, and the position of the antipodals and 

 development of the fusion nucleus follow the common program 

 found in most angiosperms. The megagametophyte is surrounded 

 by a thin nucellar layer; but, at maturity, these cells degenerate 

 completely so that the fully developed gametophyte lies appressed 

 to the innermost layer of the integument. 



Variations in the development of the gametophyte have been 

 reported in this family. Nanetti (16) and Young (31), investigat- 



