igoj] Biological notes on Canadian species of Viola. 155 



The caulescent violets show but a slight variation, which 

 m restricted to the mere serration or crenulation of the leaf 

 margin. But the most conspicuous variation is to be observed 

 in V. pedata, if we compare the leaves of the mature plant with 

 those of the rootshoots. Some of these types of leaves are figured 

 on our plate (Plate V, figs. 13-16), and we notice the great 

 divergence between the normal leaf (fig. 13) and the smaller one 

 (fig. 14), which was taken from a one year old specimen. In the 

 rootshoots (figs. 15-16) the leaves show a tendency to becoming 

 almost entire, and one would hardly have suspected them to 

 belong to this species, if it were not for the fact that we succeeded 

 in preventing them from breaking off when the mother-plant was 

 lifted. 



Considering these few but well marked cases of leaf-variation 

 in Viola, we might suppose that several of the recently described 

 new species, in which the outline of the leaf constitutes an im- 

 portant part of the diagnosis, may be referred to some single 

 type with ability to adapt itself to the surroundings, and to exhibit 

 a certain amount of variation. And we must remember that 

 besides varying in leaf-outline these same species do, also, vary 

 in respect to the pubescence, which is still more influenced by the 

 conditions of the surroundings, character of the soil, light and 

 shade, etc., and it can, of course, only be ascertained through 

 prolonged study in the field whether such plants are suificiently 

 constant in their mode of growth so as to be considered as valid 

 species. 



THE RHIZOME. 



Few organs are as constant in their structure as those which 

 constitute the rhizome, the under-ground stem-portion, with its 

 leaves and roots ; yet it is very seldom that recent authors pay 

 much attention to this part of the plant, when they describe new 

 species ; in regard to Viola it is generally passed by in silence. 

 The following types of rhizome are observable in the Canadian 

 perennial species of Viola : 



A. Rhizome vertical, monopodial, leaves all basal with_ 



axillary flowers : yv^^^OAi^ 



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