igig] EVANS— PENTSTEMON 43 1 



egg apparatus had formed and polar fusion had occurred in both 



embryo sacs. False polyembryony seems to be quite common in 



this species. 



Fertilization 



In several cases the pollen tube with the tube nucleus and the 

 2 sperms were observed. While in the pollen tube the sperms are 

 more or less capsule-shaped, but after reaching the embryo sac 

 they become quite spherical. The pollen tube seems always to enter 

 the embryo sac a little to one side, its entrance usually destroying 

 one of the synergids, the other synergid disappearing soon after- 

 ward. 



The sperms are readily distinguished from the egg nucleus and 

 the polar fusion nucleus on account of their much smaller size. 

 Fertilization of the egg and the triple fusion always occur in the 

 micropylar end of the sac and in a normal manner. Both fusions 

 occur at approximately the same time. 



Several cases of double fertilization were observed (fig. 7). 

 Previously double fertilization has been announced as occurring 

 in Digitalis purpurea, Linaria vulgaris, Melampyrum sylvaticuniy 

 Lathraea squamaria, Pedicularis foliosa, and Striga lutea of the 

 Scrophulariaceae. This adds Pentstemon secimdiflorus to the list. 



Formation of endosperm 



Without resting after the fusion with the sperm, the endosperm 

 nucleus by a series of divisions forms a large number of nuclei, 

 which migrate to the chalazal end of the sac and there become 

 peripherally placed. Simultaneous with the formation of the free 

 endosperm nuclei the narrowed end of the sac begins to increase 

 in size very rapidly, so that it soon surpasses the micropylar end 

 in diameter (fig. 8). By the time the first endosperm walls have 

 formed this end of the sac is much the larger. During all this 

 increase in size a certain restricted area between the 2 ends remains 

 very narrow, so that the embryo sac comes to be dumb-bell-shaped, 

 with the chalazal end the larger. Endosperm walls continue to 

 form in this end until the whole is completely filled (figs. 8, 10). 

 Although endosperm nuclei are occasionally found in the micro- 

 pylar end of the sac, no cell walls were observed to form. During 



