78 MARGARET C. FERGUSON 



illustration of development within the embryo-sac without the 

 intervention of a spore, but these are apparently isolated and 

 exceptional cases. 



The whole difficulty seems to me to lie in the fact that all 

 along we have been endeavoring to make a morphological unit 

 out of that which is primarily a physiological unit, and not 

 necessarily a morphological one, although it may be so. It has 

 been shown conclusively that in Larix and Pinus among the 

 Gymnosperms a true macrospore is formed which germinates 

 within the macrosporangium and gives rise to the female gamet- 

 ophyte both a morphological and a physiological unit. But 

 as we advance to the Angiosperms there is a shortening of on- 

 togeny in the female gametophyte, the most extreme case being 

 represented by Lilium. Mottier ('98) demonstrated the fact 

 that the division of the embryo-sac-mother-cell in Lilium is a 

 true tetrad division and we cannot, therefore, it seems to me, 

 escape the conclusion that the resultant four cells are spores. 

 But once rid ourselves of the idea descended from Hofmeister, 

 that the mother-cell of the embryo-sac is always a macrospore, 

 and the product of its development, therefore, always a single 

 gametophyte, and many difficulties vanish. Lloyd ('02), in his 

 recent discussion of this subject, accepts the heterotypical divi- 

 sion as the criterion for spore formation, and then explains the 

 condition in Lilium^ where the first four cells of the embryo- 

 sac are spores, by " regarding the gametophyte as an individ- 

 ual by coalescence" It appears to me not only more simple 

 but more plausible to consider that we have here four gameto- 

 phytes each reduced to two cells. The embryo-sac is still here 

 as elsewhere (with the exception of parthenogenic plants), a 

 physiological unit whose function is to give rise to a new plant 

 through the sexual process, but it is morphologically a complex 

 made up of several individuals. Whether all eight cells thus 

 formed are considered as potential eggs is immaterial, practi- 

 cally, but one retains the power to respond to the sperm-cell, 

 though the others have been shown to be capable of fertiliza- 

 tion in some instances. Ordinarly, however, they remain ster- 

 ile and have come to have a vegetative or nutritive function 

 only. All work together for one end and in that sense may 



