iqiq] EVANS—PENTSTEMON ' 433 



of the way through the endosperm, where further progress is prob- 

 ably stopped by the division and growth of the embryo. The 

 first 2 di\isions of the embryo are at right angles to each other and 

 in the plane of the long axis of the sac. The next division is at 

 right angles to the first two and forms the 8-celled stage of the 

 embryo. The i6-celled stage is formed by the pericHnal division 

 of the cells of the octant. The further division of the embryo was 

 not followed. 



After the embryo becomes imbedded in the endosperm the 

 micropylar end of the sac, together with the suspensor, collapse 

 and disappear. Their disappearance is accounted for by the pres- 

 sure within the ovule, due to the increase in amount of endosperm 

 which eventually comes to occupy all the space inside the seed coat. 



Discussion 



In the formation of the embryo sac of P. secundijiorus there is 

 nothing strikingly different from that of other species of this family 

 which have been studied, but the shape of the mature embryo 

 sac is peculiar. The very bulbous micropylar end, with the long, 

 narrowed chalazal end, gives the whole embryo sac a club-shaped 

 appearance. The chalazal part of the embryo sac is never more 

 than half as wide as the micropylar end at the time of fertilization. 

 The drawings of the embryo sac of other Scrophulariaceae by 

 Balicka-Iwanowska, Schmid, and Mitchell show that there 

 is a tendency toward this shape of embryo sac in the family, but 

 none of those drawn are so striking in shape as that of the species 

 under consideration. The distance between the end of the embryo 

 sac and the end of the vascular system is at first marked. As the 

 sac later derives a large part of its nourishment through the vascular 

 system, this may account for the necessity of lengthening the sac 

 until the end comes in contact with this source of food supply. 



During the development of the embryo sac traces of starch can 

 be seen within it, and in all cases, by the time fertilization occurs, 

 large quantities of starch are present. Often it is so abundant that 

 the nuclei within the sac are partially or entirely obscured. By the 

 time the embryo has reached the endosperm the starch has all dis- 

 appeared. 



