THE GENUS EQUISETUM 



were obtained, and the section shown in Fig. 226 at once gives confirmation of the 

 diagnosis of hybridity and a reason for the abortion of the spores. Fig. 227a, from an 

 acetocarmine preparation, adds details of the pairing and shows again the large number 

 of univalents. 



In the hope of synthesizing E. litorale, prothalli of the two parent species were grown 

 in 1939, and insemination from young males of £. limosum into old females of £. arvense 

 was watched under the microscope. Unfortunately, the difficulties of culture were not 

 successfully surmounted for the later stages and all the inseminated prothalli died from 

 fungus attack. If these cultural difficulties could be overcome the synthesis oi E. litorale 

 ought to be possible. 



E. trachyodon A.Br, is known in Floras as a very rare European plant in which defective 

 spores were detected as long ago as 1864 by Duval-Jouve. It is best known from the 



Fig. 226. Meiosis in Equisetum litorale Kuhlw. in a section 

 showing lagging unpaired chromosomes, x 1000. 



Rhine valley and from Ireland, although single stations are now on record for a few 

 other countries, e.g. Scotland and Latvia (Kupfer 1929). In contrast to E. litorale, 

 E. trachyodon is very uniform morphologically wherever it is found, although Milde was 

 able to detect a few minor differences between the Irish and Rhineland specimens. 

 As in E. litorale the spores of E. trachyodon are completely aborted, and the means for 

 its very wide distribution are at present quite unknown. 



As in the previous case, my material of £. trachyodon came from Ireland. I visited an 

 east Irish locahty with Dr Praeger in June 1938, and fixed wild cones, but this particular 

 plant cones also readily in cultivation and abundant material is easily obtained. The 

 principal results are perhaps sufficiently shown by Figs. 227 <: and d, representing 

 diakinesis and metaphase (or anaphase) respectively. The almost complete absence of 

 any sign of pairing is the most characteristic feature, although a solitary bivalent can be 

 seen on the spindle in Fig. 22 7^. 



Failure of pairing on this scale is the obvious explanation for abortion of spores, and 

 it is not, in fact, more extreme here than in some other well-authenticated wild hybrids, 

 notably some of the triploid ferns such as the Polypodium of Fig. 139. It should, 



228 



