XIII EQUISETJNEyE 457 



sporangia begins nearly a year before the spores are shed, and 

 they are completely developed during the preceding autumn. 

 The growth of the fertile branch and the scattering of the 

 spores take place very soon after growth begins in the spring. 

 Whether in cold climates E. telniateia behaves the same way 

 I cannot state ; but in California, where growth continues all 

 the winter, the development of the sporangia is gradual, and 

 the fertile stems grow up and scatter the spores as soon as 

 they are ripe. The ripe sporangia are oblong sacs, whose wall 

 is composed for the most part of a single layer of elongated 

 cells, marked with spiral thickened bands upon the dorsal 

 surface and rings upon the ventral cells, where the longitudinal 

 slit by which the sporangium opens is placed (Fig. 241, D, E). 

 The internodes in the strobilus are very little developed, but as 

 the spores ripen there is a slight elongation, by which the 

 sporophylls are separated. 



Classification 



Milde ^ divides the genus into two, Equisetum {Equiseta 

 phanopora), in which the accessory cells of the stoma are on a 

 level with the surface of the epidermis ; and Hippochczte (E. 

 cryptopora), in which the stomata are sunk in depressions of the 

 epidermis. In the former group are two divisions, those which, 

 like E. arvense and E. telmateia, have the fertile and sterile 

 bra,nches different, and those where they are alike, e.g. E. liinosuni 

 (.Fig. 242, A). In the former group some species, e.g. E. pratense, 

 have the fertile stems at first colourless, but afterwards forming 

 chlorophyll and developing branches. In Hippochcete, which 

 includes among American species E. Jiiemale, E. robustum, E. 

 variegatum and E. scirpoides (Fig. 272, B), the aerial branches 

 are all similar and often are quite unbranched. The foliar 

 sheaths show considerable variation. In the fertile stems of E. 

 telniateia (Fig. 227) they are extremely large and the ribs very 

 prominent, but the separate leaves are not all distinct at the 

 apex, but the sheath splits into a few very deeply cleft pointed 

 lobes. In the sterile shoots, however, and in all the stems of 

 most species, the teeth are very distinct and the foliar sheath 

 much shorter. The number of teeth varies from three in 



1 Milde (I). 



