338 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



When the axis of the ovule forms a right angle with that 

 of the flower the archesporial cell has elongated, keeping 

 pace with the elongating nucellus, and its nucleus has 

 undergone one division (fig. 14). The cell is densely 

 filled with granular protoplasm; no vacuoles are visible. 



There are in Avena as in Eichhoniia (W. R. Smith, 

 1898) apparently three ways in which the sister cells may 

 be formed. In the first, the nucleus of the archesporial cell 

 divides after the elongation of the cell, the two resulting 

 nuclei divide, and the four sister nuclei lie free in the pro- 

 toplasm of the cell, no walls separating them (fig. 15). 

 Or (second) after the nuclei have divided, walls may 

 appear between them (fig. 17). However, owing to faulty 

 methods of staining, I could not in every instance be sure 

 of the presence or absence of the separating walls, but the 

 phenomena were observed at various times during the 

 course of the study. In the third manner of formation of 

 sister cells, dividing walls followed each nuclear division as 

 in the section represented in figure 16. This variation in 

 the formation of sister cells was not described by Koernicke 

 for Triticam, or by Fischer for any of the grasses studied 

 by him. Fischer did however describe a condition in the 

 genus Melica which he says is constant, and is analogous 

 to what has been described above for Avena. In Melica 

 the division of the nucleus of the archesporium is followed 

 in all cases by the formation of a dividing wall. The two 

 nuclei thus formed divide each once, but without cell- 

 walls being formed; so that in Melica there are two cells 

 with two sister nuclei in each cell. It would be of import- 

 ance to know whether this condition is as constant as 

 Fischer states, or whether there really is in Melica that 

 variation in the formation of the sister cells which is appar- 

 ently the case in Avena and in Eichhornia. 



In whatever way the sister cells are formed four super- 

 imposed nuclei always result, and of these the lowest 

 becomes the spore mother-cell, the others becoming 

 resorbed. The uppermost of the sister cells is the first to 

 disappear (fig. 17), and after it the two next lower ones in 



