434 EQUISETUM LESS. 



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 Lessons. 



EQUISETUM 



The horsetails are common British plants found usually 

 in moist or marshy situations, and reaching a height of 

 i to 3 feet. 



The plant consists of a branched underground stem or 

 rhizome, lateral branches of which grow vertically upwards, 

 and constitute the aerial shoots. Both stem and branches 

 have a very characteristic appearance : they are distinctly 

 segmented or divided into nodes and internodes, and from 

 each node springs a crown-like structure or leaf-sheath 

 (Fig. 112, A, and Fig. 113, A, /. sk\ formed by a whorl of 

 leaves united into a continuous structure. In some cases 

 the aerial shoots also give rise to secondary shoots (Fig. 112, 

 A, sh\ arranged in whorls and apparently arising below the 

 leaves : actually, however, they originate in axillary buds, as 

 in Nitella, but, instead of growing out between the stem and 

 the leaf, perforate the base of the latter. 



The internodes of both rhizome and aerial shoots are 

 hollow, each having a large axial air-cavity (Fig. 112, B, c l ) 

 extending throughout its whole length, and formed by the 

 disintegration of the central parenchyma-cells of the young 



