78 .MORPHOLOGY OF ANGIOSPERMS 



fenbachia, of the same family, Campbell 75 states that the inner 

 one of the two cells may divide, forming a row of three mega- 

 spores. Among the Pontederiaceae, Smith 53 found great varia- 

 tion in the development of the megaspores. While sometimes 

 the row of four is formed by equal successive divisions, it is 

 more common for the mother-cell to elongate greatly, with its 

 nucleus near the micropylar end. In this position two succes- 

 sive and rapid divisions of the nucleus occur in any order or 

 direction, and four usually naked cells are the result, the inner- 

 most being much the largest and speedily obliterating the others, 

 becoming the functioning megaspore (Fig. 29, B). In Arena 

 fatua, Cannon 86 found that four cells are formed; or the 

 mother-cell may contain four nuclei without any cell walls, the 

 three outermost disappearing, the innermost forming the nu- 

 cleus of the functioning megaspore. In Potamogeton foliosus, 

 Wiegand °° found that the second divisions in forming the row 

 of four are not accompanied by walls, and Holferty •'" found in 

 Potamogeton nutans that the outermost wall may not appear 

 even when there is nuclear division. Such cases emphasize the 

 fact that there may often be the greatest variation in the devel- 

 opment of megaspores, and that a number reported for a species 

 by a hasty observer should not be regarded as a fixed one, el- 

 even possibly the customary one. 



The only generalization that seems to be safe in reference 

 to the Monocotyledons, aside from the fact of their great irregu- 

 larity, is that more of them than of the Dicotyledons have 

 reached the condition of an undividing mother-cell. 



Among the Archichlamydeae, nearly all the species investi- 

 gated have three or four megaspores, and both of these numbers 

 are represented in almost every family in which more than one 

 species has been studied. Upon the whole, however, a row of 

 three megaspores seems to be more common than one of four. 

 For example, among the Ranunculaceae, of eleven genera stud- 

 ied only four have been reported as having four megaspores, and 

 in all of these cases three megaspores have also been observed. 

 The four genera referred to are Aquilegia, in which five mega- 

 spores were also observed, Delphinium, Ranunculus (Fig. 27), 

 ami Thalictrum, and in each of these eases different observers 

 have given different numbers. In Caltha, which ordinarily has 

 three megaspores, Mottier 36 occasionally found nuclear divi- 



