ii8 The Irish Naturalist. [May, 



quite unbranched, like E. hycmalc ; but more frequently 

 branches, which may be quite short, or may overtop the main 

 stem, spring from the nodes, often singl}', and never in whorls ; 

 and some of these usually bear fruit. 



To turn now to the Horsetails which produce special fruit- 

 stems. E. sylvaticum, the beautiful Wood Horsetail, can 

 hardly be reckoned among these, but it furnishes a connecting 

 link, since the fruit matures before the prettily divided green 

 branches, and when the latter are fully grown the fruit is 

 shrivelled and dry. 



E. pi^atejise, a rather local species, is a connecting link of 

 a more pronounced type. The fertile stems, which appear 

 in early spring, are quite unbranched at first, but eventually 

 develop short green branches, shorter than those of the later 

 barren stems. The fertile stems are, as in the two species 

 next mentioned, shorter, and have larger sheaths, than the 

 barren stems. 



In E. arve7isc, the verj^ common Field Horsetail, and E. 

 7naxhmi7n, the Great Horsetail, the fruiting-stems are quite 

 different in appearance from the barren ones, being short, 

 unbranched, with large loose sheaths ; they are coloured 

 pink and brown, and are mature in the month of March or 

 April. The barren stems are taller, with close sheaths, and 

 numerous whorls of green branches, and are not mature until 

 a month or more after the fertile stems. Here we have a 

 division of labour, the fertile stems devoted to bearing the 

 spores at the time and place which is most advantageous, the 

 barren stems appearing later to perform the process of assimi- 

 lation when the conditions of light and heat are more favour- 

 able. 



The stems have been specialised to best perform their respec- 

 tive functions, and they now differ not only in size and 

 appearance, but also in the season of their maturity. This 

 being so, it is to be expected that departures from these 

 t3'pes, or intermediate forms, will be rare. In E. arvensc, the 

 all- too-common Field Horsetail, the barren stem varies much 

 in shape according to the situation in which it is placed, but 

 the fertile stem is very constant. I have never noticed any 

 aberration in the latter, nor any instance of a stem of inter- 

 mediate character, but instances of the latter do occur, and 

 constitute the variety ca^npesire of Schultz. In E. maxi77tnm 



