DR YOPTERIS CRIS TA TA x MARGIN A LIS. 7 



The general outline of the fronds of this fern and of the fronds of 

 D. Boottii are frequently very similar, and the two ferns at a short 

 distance often bear a striking resemblance to one another, but on 

 closer inspection the likeness vanishes. There is not much danger of 

 confusing cristata iiiarginalis with marginalis. The color of the 

 fronds — deepening in shade and something between a yellow-green 

 and a blue-green — is alone sufficient to distinguish it at once from 

 marginalis., and there are other differences easily seen on comparing 

 the two. 



I do not know whether cristataxwarginalis really approaches 

 cristata more nearly than it does marginalis., or whether the difference 

 between it and marginalis is of a kind more readily seen than the dif- 

 ference between it and cristata., but there is certainly sometimes 

 difficulty in distinguishing between the two latter. Cristata, like 

 cristata marginalis., is very variable, and there is apparently a perfect 

 transition through intermediate forms from one to the other; I am 

 not sure that there is a transition in reality. If, in a plant with inde- 

 terminate fronds, the growth of the rootstock is clearly terminal or 

 clearly lateral, there is no doubt as to which of these two species the 

 plant belongs; but a plant may have lost some of its fronds and its 

 rootstock may be bent, so that the growth appears lateral when really 

 terminal. Fortunately this is unusual. No one could possibly mis- 

 take a typical specimen of either fern for the other. Even when a 

 specirnen is not typical and seems to be neither clearly the one fern 

 nor the other, but an unhappy compromise, the distinctive features of 

 one usually predominate ; what might be called the personality of the 

 one is more strongly present than that of the other. Which perhaps 

 means simply that in this, as in other things, the scales rarely balance, 

 they tip — now this way, now that way. 



The known stations for cristataxmarginalis are New London, 

 Conn. ; Boxford, Newbury, Merrimac and Medford, Mass. ; Warren, 

 R. I. ; Pittsford, East Peak and Chittenden, Vt. ; Hampton Falls, N. 

 H. ; Summit, N. J. ; and Dover, Me. 



It has been estimated that a single plant of the Russian thistle 

 (Salsola Kali Tragus) six feet in diameter produces 2,000,000 seeds. 

 These plants break away from the roots in fall and winter, and are 

 rolled and tumbled by the winds over the frozen ground, scattering 

 the seeds for miles. By a curious device the seeds are held in the 

 axils of the bracts by two minute tufts of coiled hairs, which prevent 

 the seed falling out at once when the weed begins to roll, the whole 

 being a most perfect adaptation for the widest possible dissemination. 



