THE GENUS EQUISETUM 



however, be noted that complete failure of pairing can sometimes be produced by other 

 means, either metaboHcally or owing to an asynaptic mutation. If the latter were the 

 case here, however, it is difficult to see why an asynaptic mutant should be the only 

 representative of a species to survive and positive evidence for the former is wholly 

 lacking. Indeed, in an attempt to alter the grade of chromosome pairing experimentally, 

 a piece of the plant was transferred to a hot greenhouse and maintained at tropical 



1 # 







Fig. 228. Spiral structure at anaphase of the first meiotic division 

 in Equisetum trachyodon A.Br, x 2000. 



temperatures (70° F.) for over two years without the slightest effect. A hybrid origin 

 therefore remains the most probable explanation for it, and the most probable parents 

 in that case are E. variegatum x E. hiemale.* 



In spite of the absence of experimental proof of the suggested parentage of £■. trachyo- 

 don there would probably be little reason to look elsewhere for a mode of origin but for 

 the circumstance that the third case of an apparent hybrid, E. Moorei, seems to relate 

 to the same two species, although it is itself quite unlike E. trachyodon in habitat and 

 appearance. E. Moorei is a maritime plant of sandy soil found for about 100 miles along 



* A relationship with the south European E. ramosissimum has sometimes been suggested, which I was 

 at first inclined to disregard since this species was thought not to be British. I have however recently been 

 informed by Mr. A. H. G. Alston of the British Museum that an authentic specimen of is. ramosissimum 

 has recently been found in Norfolk and it may therefore perhaps also have existed in Ireland in former 

 times. If this were so it would greatly assist the problem of finding suitable parents for both E. trachyodon 

 and E. Moorei in that country. 



230 



