1474 



A TEXTBOOK OF THEORETICAL BOTANY 



Fig. 1352. — Anomalous embryo formation. A, Fiinkia (Hosta) ovata. Weak embryo from 

 the oosphere, two adventitious embryos growing from the nucellus. B, Erythroniiim 

 americantim. " Embryogenic mass ", arising from basal cell of the divided zygote, 

 forming four embryos. C, Allium odoniin. Three embryos derived from antipodal 

 cells. D, Naias major. One embr\o from the oosphere, the other from a synergid. 

 E, Alchemilla pastoralis. One embryo from an unfertilized oosphere, another arising 

 from the nucellus. (From various sources.) 



embryos. This has been seen in Allium odoriim, FAatostema (Urticaceae) 

 and in Uliniis, where the antipodal cells resemble oospheres (see Fig. 

 1333). The subsequent fate of these embryos is not known, but their 

 survival is improbable. 



Doubling of the embryo sac in one nucellus occasionally happens, where 

 the archesporium is multicellular and more than one cell develops into a 

 mature sac (Fig. 1353). Instances have been previously cited. The develop- 

 ment into embryo sacs of more than one megaspore of the normal tetrad 

 is also not uncommon, e.g., Poa alpina. Usually competition limits the 

 further development of all but one of the sacs present and polyembryony 

 of the seed has not been definitely traced to such an origin. 



All other cases, where embryos arise adventitiously, i.e., outside the 



