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out a State and exposed to conditions that in time would 

 produce some differences in the length of the leaves, the 

 number of stomata, etc. Under such circumstances it is 

 fair to assume, from the analogy of other fernworts, that 

 the spores would be among the last to change their char- 

 acters. If the extremes of the vegetative parts, how- 

 ever, were selected as characters for the erection of new 

 species, it is easy to see that the spore markings would 

 not present differences that would be specific. This view 

 of the matter seems borne out by the case of /. riparia and 

 /. saccharata, which, though much alike, have until re- 

 cently been considered distinct species. Now, however, 

 there are many who look upon them as but two strongly 

 marked races of the same species. Even those who deny 

 that spore-characters are of great value in separating 

 species, freely admit that this single feature is the best 

 indication of family relationship that we have. Let a 

 species be found with spinulose spores, and it is sure to 

 be referred to the /. echinospora group, while one with 

 crested spores will be referred to either /. Engehnanni or 

 /. Tuckermani. In my own opinion the time will come 

 when several of the western species will no longer be re- 

 garded as such, but more properly placed as varieties of 

 others. Mr. Dodge has shown that the spore-walls are 

 composed of silex. In the other fern allies (Equise- 

 tacccu) in which depositions of silex are found, the ar- 

 rangement of the deposits has been often considered suffi- 

 cient for separating species, notably in the case of Equise- 

 tum robustum and E. hiemale. The question then arises, 

 why is it not proper to rely upon this character in Isoetesf 

 As to the size of the spores, much of what has been said 

 of leaf characters applies here. If the plant is vigorous 

 it is to be expected that its spores will be somewhat dif- 

 ferent in size from those of less robust specimens. There 

 are limits, however, beyond which the spores do not prop- 

 erly vary, and a plant that constantly produced much 

 larger or smaller spores than others with similar mark- 

 ings might with propriety be separated as a variety or 

 species. So far from considering spore-markings as un- 



