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HABITAT. 



This species, though abundant where found at all, is quite 

 sporadic and rare. It was first discovered at St. Petersburg 

 about 1845, but its range has been extended over Europe and 

 eastern America from about 49-60' N. lat. It has not yet been 

 reported from Asia. In America, so far as available material 

 shows, it extends from Pennsylvania to Maine and Ontario west 

 to Minnesota. Reported from Washington and British Colum- 

 bia, but Suksdorf's and Macoun's plants so labeled are fiuviatile. 

 It is probably much more common than is suspected, as it grows 

 with and greatly resembles fiuviatile, for which the general col- 

 lector will take it. 



Along the lower course of the Merrimac river for miles it is 

 an abundant and characteristic plant, and under the name of 

 "joint-grass" is cut for hay. It is the only species which I have 

 seen growing wherever influenced by salt water, it growing on the 

 border of marshes at Salisbury, Mass. 



HYBRIDITY. 



This species is commonly regarded to be a hybrid between 

 arvense and fiuviatile, as it stands exactly between them in struc- 

 ture and habit, and the fruit is abortive. If so it would not be a 

 difficult thing to prove, for Equisetum prothalli being dioecious, 

 the almost insurmountable obstacles in the way of fern hybridiza- 

 tion would be evaded. It would be a good subject for under- 

 graduate investigation. Milde at first considered it to be a 

 hybrid, but later receded from his position and left the matter in 

 doubt. Buysson, in his monograph, strongly combats the idea. I 

 am not aware that any American author nas ever written on the 

 subject. If a hybrid, its range should be co-extensive with the 

 range of its parents, which does not appear to be a fact. The 

 spocies of arvense ripen at least a month before those of fiuvia- 

 tile, and from its habit they would not be expected to germinate 

 where fiuviatile cou d fertilize it. But the prothalli are quite 

 persistent, at least female ones, so difference in time of fruiting 

 would not necessarily debar hybridity, and in seasons of low 

 water the prothalli might grow in quite low places till fertilized 

 and rooted. Milde offers as an objection, the fact that new 

 plants from spores are comparatively rare in this genus, it being 

 a good exatnp e of the universal fact that plants easily multiplied 

 by other metnods than by seed get to depend on that method and 



