—45— 



appearance. This is seldom regarded as of specific im- 

 portance. It appears to be fairly characteristic of the 

 whole group the difference between species being a matter 

 of greater or less spotting. 



Bast-Bundles. — In these plants, as in all others, the 

 bast-bundles aid in holding the parts erect. In all species 

 some bast is present, but it is best developed and the 

 bundles are most numerous, as would be expected, in the 

 species whose leaves are often exposed to the air. The 

 leaves of the submerged species, buoyed up by the water, 

 have very little bast. Since the amount of the bast de- 

 pends upon the exposure of the plant, it is perhaps pos- 

 sible to make too much of this feature as a specific 

 character. 



The Spores. — In " Fernwort Papers " Mr. A. A. Eaton 

 observes : " I know of no character more unreliable than 

 the sculpture of the spores." With this I cannot agree. 

 Not only does the spore sculpture seem to me to be fairly 

 stable in each species, but this single feature is very char- 

 acteristic of whole groups. A curious connection be- 

 tween temperature and spore markings also seems to exist 

 among North American species at least. In New Eng- 

 land, there is not a single species in which the spores are 

 marked by roundish warts or dots. They are all charac- 

 terized by spines, ridges or anastomosing crests. As we 

 go southward, however, we find /. melanospora with faint 

 warts that suggest the remains of spines and ridges, while 

 westward, the species are, without exception, marked by 

 dots or warts, until Washington and British Columbia is 

 reached, when we again find species with spinulose spores 

 as in New England. That these markings are influenced 

 merely by temperature is doubtless untrue, but so far as I 

 know, no better reason for these differences in markings 

 has been suggested. 



That the markings of the spores are inclined to pre- 

 sent intergrading forms between what we now regard as 

 species, may be a true gradation, or it may possibly hap- 

 pen that our conceptions of the species are incorrect. It 

 is possible to imagine a certain species growing through- 



