THE GENUS EQUISETUM 



main branches from which the laterals were emerging having presumably been fertile 

 earlier in the year. 



Fundamentally different habits are met with in those species which bear their cones 

 either on separate short, colourless shoots or on special colourless apical portions of 

 green shoots. These species are E. arvense, E. maximum, E. pratense of the first type and 

 E. sylvaticum of the second. All these four species shed their spores very early in the 

 spring (March or April), in the first three cases before any green vegetative shoots are 

 visible, and maturation of the spores in each is completed in the previous autumn. 



Since the cones of these species are perhaps less familiar in autumn than they are 

 in spring, a photograph, natural size, of E. maximum, dug up in late September, is re- 

 produced in Fig. 212. At this time structurally perfect green spores are already present 

 in the fat winter buds which enclose and protect the dormant cone under many sheaths 

 of russet brown scales. The buds, two of which are seen in the figure, project an inch 

 or more above the ground, and are as a rule to be found near the base of a standing 

 green shoot of the current year. The base of this is seen to the left of the cone buds, 

 and if both it and the buds are traced down to their origin it can be seen that both 

 arise as lateral branches from the base of a still older shoot of the previous year. The 

 habit of spring shedding of spores seems therefore to represent a delay in the liberation 

 of spores which morphologically belong to the year in which meiosis occurs rather than 

 to precocious development. 



Meiosis takes place in these cone buds in early September, when they are already 

 above ground but not at their full size. The cone is easily exposed by sphtting the bud 

 or by peeling off the sheathing leaves. It is soft, white and juicy when meiosis is occur- 

 ring, becoming yellow with greenish sporangia when the spores are complete. In the 

 young stages the cones seem to be very attractive to small animals which I take to be 

 mice, since they are often found partly or completely eaten away. 



Although the cone buds in all four species {E. arvense, maximum, pratense and sylvaticum) 

 are actually above ground at the time of meiosis and may be found readily enough by 

 careful examination of the soil surface near the base of a standing shoot, it is in practice 

 unprofitable to do this unless a coning site has first been marked down with some accur- 

 acy in a previous spring. In every species very large areas of ground may be occupied 

 by vigorous but sterile populations. Good coning sites seem to be topographically deter- 

 mined as places with rather better drainage and fuller illumination than those which 

 suffice for vegetative growth. This is perhaps the reason why E. arvense is so often found 

 to cone abundantly on railway banks. Once a coning site has been detected, fertile plants 

 will recur there year after year with unfailing regularity, unless the ecological conditions 

 alter. The problem of finding fertile material of E. arvense, maximum, pratense and 

 j^/ya^icM/n is then not difficult.* 



Within the cone itself the order of maturation of the various parts is the same in all 

 species. The first sporangia to mature are those in the widest part of the cone, and de- 



* The sites actually used for this work were : for E. arvense, a dump of disused builders' sand in a meadow 

 near Stockport; for E. maximum, the raised bank of a canal near Stockport; for E. sylvaticum, a clearing in 

 a steeply sloping wood near Stockport ; and for E. pratense, a well-drained east-facing rock garden in the 

 grounds of Westonbirt Girls' School, where this rare species has become established and cones annually. 



214 



