Ra 3 f 
{ 
Special Morphology and Classification. | 321 
and serving, by their hygroscopic properties, to assist in 
their dissemination]. On germination the spore gives rise 
first to a flat pro-embryo or prothallium, upon which are 
produced, in some species only one, in others both kinds of 
reproductive organs, antheridia and archegonia (Fig. 445) ; 
? | III. 
Fic. 445.—Lguisetum maximum; 1. prothallium v with eleven antheridia a (x 30) ; 
II. prothallium v with archegonium a (x 30); III. an antherozoid (x 500). 
the former species being therefcre dicecious, the latter mon- 
cecious. In the antheridia are developed a number of 
motile antherozoids ; in the archegonia, as in Mosses, a 
single central cell containing an oosphere, which, after 1m- 
pregnation, developes gradually into the young plant. ‘The 
alternation of generations is therefore precisely similar to 
that of Ferns. The Equisetaceze are also propagated ina 
vegetative non-sexual manner, by means of subterranean 
stolons and tubers (Fig. 443 Iv., p. 318). 
The class includes only a single genus, Lgutsetum. A quantity of 
silica is deposited in the stems, and especially in the epidermis ; £4. 
Y 
