- 4 8- 



lobed cap, beneath which are borne the sporangia, which, when 

 ripe, rupture and disseminate the spores. 



A little observation among growing plants will convince one 

 that the spike is a stem arrested in development. Sometimes an 

 internode in the spike will become lengthened, bearing a normal 

 sheath, thus forming two spikes in series, and I have even found 

 them with branches below the upper spike. In several of the true 

 Equiseta the spike may end in a proliferous point, like the end of a 

 sterile stem ; and I have seen arvense with about half a normal 

 spike, bearing on its top three inches of normal-branched stem. 



That the clypeoles are modified teeth may be seen by hunt- 

 ing among arvense and siivaticum for transitional forms of the 

 ring beneath the spike, when they may often be found with cly- 

 peoles and teeth intermixed. 



The spores are green, globular bodies, very similar in all 

 species. They bear two bands, fastened together in the middle 

 at right angles. The free ends, ending in a broad expansion, are 

 spirally wound round the spore. These are very hygrometric, un- 

 winding when dry, but coiling tightly round the spore when moist- 

 ened, as by the breath. These undoubtedly assist the spores in es- 

 caping from the sporangia, and possibly in inserting them in places 

 suitable for germinating. The vitality of the spore lasts only a short 

 time, usually less than three days. If sown on water or damp 

 earth they readily germinate, though those on water usually fail 

 to become established as plants. The development of the pro- 

 thallus by division of cells, the formation of archegonia, ultimately 

 fertilized by the little wriggling antherozoids, are much as in the 

 ferns proper. The prothallia are several-lobed, and usually uni- 

 sexual, so it is necessary, in order to secure fertilization, for pro- 

 thallia of both sexes to be contiguous. 



The inner structure of the stem is peculiar. In all there is a 

 hollow in the center, extending the length of the internode ; in 

 some species very large, in others very small or obsolescent. In 

 cross section this is surrounded first by loose parenchyma cells, 

 then directly under each ridge there is a small opening (carinal), 

 surrounded by bast-fibers, which layer extends from these to the 

 epidermis. Between these carinal openings, but usually a little 

 nearer the exterior, there are larger openings (vallecular), situ- 

 ated directly under the grooves. The outer part of these has a 

 coat of chlorophyl, usually showing as two distinct areas, between 

 which the stomata open into the cavity. Thus the vallecular 



