﻿ioi6] GATES— PAIRS OF SPECIES 181 



spherical to elongate, irregular, or lobed. In a few plants of this 

 species the embryo sac develops normally, followed by fertilization 

 and the production of embryos, but the embryos always possess 

 an apical protuberance which is lacking in the polyembryonic 

 embryos of apogamous plants. The exact manner of origin of 

 the apogamous embryos was not determined, but it appears that 

 individual plants produce embryos which are either all apogamous 

 or all resulting from fertilization. This matter is worthy of further 

 study. No other orchid is known to exhibit this type of poly- 

 embryony, although twin embryos occur in many species; but the 

 latter are believed to result from a doubling of the embryo sac 

 followed by fertilization by two pollen tubes. These facts are of 

 interest because it is known that tetraploid species are frequently 

 apogamous. 4 



It has also been observed 5 that a peculiar form of vegetative 

 multiplication takes place in 5. cernua, in which young plants are 

 produced from the root tips, but in this case a similar development 

 was reported by Strasburger in Neottia sp. 



Another interesting point is the manner in which light is thrown 

 on relationships by cytological study. The mutation theory is 

 destined in this way to modify many current taxonomic conceptions 

 of relationship. Spiranthes cernua in the manuals is separated from 

 5. gracilis by several other species, yet it must have been derived 

 at some time from this or possibly from one of the other diploid 

 species. It is even possible, as Miss Pace suggests, that S. cernua 

 may still be arising by sporadic mutations from S. gracilis. Both 

 species have much the same range, from Nova Scotia to Manitoba, 

 Florida, and Texas. The borders of distribution of this pair of 

 species are nearly, if not quite, coterminous. 



Clintonia borealis (Ait.) Raf. and C. umbellulata 



(MlCHX.) TORR. 



As regards distribution, Clintonia borealis is more northerly and 

 much more widely distributed than C. umbellulata. It occurs 



and Co. iqi S ( pp . I97 ff.). 



5 Hall, J. G., Vegetative reproduction in SpiratUhes cernua. Rhodora 7:40-5°- 

 fig- 1. 1905. 



