76 Rhodora [April 



wide range of variation in size is due to the same phenomena that 

 govern in the ease of S. ccrnua. 



In another paper of this series I shall show that Pogonia verticiliitta 

 (Willd.) Nutt (Isotria vcrticillata Raf.) in its seedling stages de- 

 velops, in its first or second season of growth, a very weak root- 

 system and only three leaves, and that this species probably requires 

 a long preparatory period before the plants are strong enough to 

 produce their first flowers. It is on this basis that we may explain 

 the general similarity among the flowering plants of a colony of 

 this Pogonia when compared with a colony of Spiranthes ccrnua 

 in which a striking dissimilarity is apparent in floral and vegetative 

 characters. We do not find here a succession of flowers produced 

 during the early stages of development of the plants. Variations, 

 if they occur, must be explained as the result of unusually favor- 

 able or unfavorable conditions affecting a plant here and there, 

 or as the breaking down of specific characters, because in this case 

 we are in the presence of a species that attains vegetative maturity 

 before it begins to form its flowers. 



The most favorable time to study the seedling stages of Spirant lies 

 is in the summer and autumn when the different species are flower- 

 ing. The reason for this is explained by the tendency of the seeds 

 to germinate near mature plants. It would seem that the mycor- 

 rhizal fungus usually associated with S. ccrnua and perhaps essen- 

 tial to its development, is in abundance near established plants and 

 ready to infect fertile seeds. The parent plants also serve as a guide 

 to the places where seedlings may be sought for with success. Care- 

 ful search will sometimes reveal hundreds of young plants in many 

 stages of early development from the protocorm, devoid of root or 

 leaf, to seedlings with a well developed root and one or more leaves. 

 In an area less than a meter square I have found literally hundreds 

 of seedlings, some of the smallest with the first leaf just forming and 

 the protocorm resting in loose humus surrounded by cobweb-like 

 hairs. In this stage of development sections of the protocorm ex- 

 hibit a very thrifty condition of the mycorrhizal fungus which fills 

 the cortical cells surrounding the vascular system. 



Although it is highly probable that Spiranthes, like most of the 

 other orchid genera that have been studied, depends on mycorrhiza 

 for successful development, it is interesting to note that mature 

 plants of Spiranthes ccrnua L. C. Rich., S. gracilis Beck, and S. 



