THE GENUS EQUISETUM 



The three cases of hybrid Equisetum available to me were all provided either by, or 

 with the help of, Dr Praeger of Dublin. Two of them, E. litorale and E. trachyodon, were 

 known to be hybrids from the literature, the third, E. Moorei, was expected to be a pure 





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Fig. 222. Two additional small-chromosomed species of horsetail for comparison of sizes and shapes 

 with Figs. 213 and 215. x 1000. a. Equisetum limosum L. diakinesis in a Feulgen squash. For 

 explanatory diagram see Fig. 223. n- 107-108. b. E. palustre L. diakinesis in acetocarmine showing 

 more usual size appearance with this technique in contrast to the exceptional degree of 

 enlargement shown in Fig. 2i8Z». c. E. limosum, metaphase for comparison with the large- 

 chromosomed species shown in Fig. 213^. 



species or subspecies, and it was with considerable surprise that unmistakable cytological 

 signs of hybridity were discovered in it. 



It will be convenient to consider E. litorale first. This plant (Fig. 224), first found in 

 central Europe, was regarded as a probable hybrid between E. arvense and E. limosum 

 by Milde in 1867 on the ground both of its intermediate morphology and its abortive 



224 



