84 MORPHOLOGY OF ANGIOSPERMS 



the spores, and it is consequently these which must be regarded 

 as the first term of the new generation." 



In case the mother-cell divides, only the innermost mega- 

 spore functions, its growth involving the digestion and absorp- 

 tion of the other megaspores, as well as more or less of the sur- 

 rounding sterile tissue. Ordinarily the elongating megaspore 

 encroaches upon the others until they become merely a cap upon 

 it; but among the Ranunculaceae Guignard 12 found in Cle- 

 matis and Helleborus, and Mottier 3G in Delphinium, that the 

 nucellus elongates so rapidly that the sterile megaspores are 

 not crowded into a cap, but their disorganization leaves a nar- 

 row cavity. The same thing occurs in Jeffersonia, as shown 

 by Andrews, 37 and doubtless among many other Archichla- 

 mydeae. The known exceptions to the functioning of the inner- 

 most megaspore are so few that they deserve special mention, 

 as possibly indicating some peculiar condition. 



Among the Monocotyledons, Agraphis (S cilia) and Dieffen- 

 bachia are the only exceptions we have noted. In the former, 

 Treub and Mellink 10 observed that the outer one of the two 

 megaspores becomes the embryo-sac, but the inner one also de- 

 velops a sac to the four-nucleate stage, an observation later con- 

 firmed by Guignard 12 for other species of the genus. In Agra- 

 phis nulans Vesque 4 observed the uppermost of a row of three 

 megaspores functioning, but the ordinary divisions within the 

 embryo-sac, up to four nuclei, were also observed in two or 

 even all of the megaspores. The same observer also reports 

 that in Yucca gloriosa all four megaspores show sac tendencies, 

 while in Uvularia each spore in a row of two developed an 

 embryo-sac to the four-nucleate condition. In Dieffenbachia, 

 Campbell 75 says that the mother-cell divides very unequally, 

 the outer one being the larger and developing the embryo-sac. 

 In Galtonia candicans (Liliaceae) Schniewind-Thies 95 has ob- 

 served an interesting transition 4o the condition of Lilium and 

 similar forms. The mother-cell usually gives rise to a row of 

 four megaspores, but occasionally only two spores appear, one 

 of which may pass over directly into the embryo-sac. 



Among the Archichlamydeae, in Juglans cordiformis (Kar- 

 sten 115 ), the two chalazal megaspores may both develop em- 

 bryo-sacs; the outermost megaspore of the row often functions 

 in Stellaria Holostea (Vesque 4 ) and in Rosa, and sometimes 



