366 EQUISETUM LESS. 



plants, reproduce by means of seeds, structures which differ 

 from spores in the fact that each contains an embryo plant 

 in the phyllula stage. 



The Gymnosperms, or naked-seeded Phanerogams, include 

 the cone-bearing trees, such as pines, larches, cypresses, &c., 

 as well as cycads and some other less familiar forms. A 

 general account of this group will be given. 



The Angiosperms, or covered-seeded Phanerogams, include 

 all the ordinary flowering plants, as well as such trees as 

 oaks, elms, poplars, chestnuts, &c. A brief description of 

 the general features of this group will conclude the lesson. 



EQUISETUM 



A horsetail consists of an underground creeping stem 

 from which vertical shoots are given off. Some of these 

 bear only leaves and branches, others are peculiarly modified 

 and produce sporangia. 



A fertile or sporangium-bearing shoot terminates distally 

 in a conical body (Fig. 84, A), formed of closely-fitting 

 hexagonal scales (sp.pti). Each scale (B, sp.ph) is attached 

 by a stalk to the axis of the shoot, and bears on its inner 

 surface a number of sporangia (spg). The scales are 

 modified leaves, and since they alone produce sporangia 

 they are distinguished from the ordinary foliage-leaves as 

 sporophylls. 



The spores, which have the same general structure as those 

 of ferns, are liberated by the bursting of the sporangia, and 

 germinate, giving rise to prothalli. But instead of the 

 prothalli being all alike in form and size and all monoecious, 

 some (c) remain small and simple, and produce only 

 spermaries (spy}-, others (D) attain a complicated form and 

 a length of over a centimetre, and produced only ovaries 



