HORSETAILS 195 



branches arise at the joints; they are equal in 

 number to the leaves of the whorl, but are placed 

 between them and not in their axils, thus differ- 

 ing from the branches of the higher plants. They 

 grow out through the leaf-sheath, by which they 

 are enclosed when in the bud. The roots grow 

 from the bases of some of the branches of the 

 underground stem; the branches which bear the 

 roots do not usually develope further. 



The fructification is always in the form of 

 very conspicuous cones, quite different from the 

 ordinary branches. 



Internally, the structure of the stem is much 

 like that of an herbaceous Dicotyledon there is 

 a ring of separate vascular strands, each of which 

 runs out at the joint into the leaf-sheath, one 

 strand corresponding to each tooth or leaf. The 

 pith is hollow in the main stem and princinal 

 branches; there is also a canal on the inner side 

 of each vascular strand, and often another sys- 

 tem of canals in the cortex. Very little wood is 

 developed, except at the joints of the stem, 

 where it connects the vascular strands into a 

 continuous ring. 



The roots have essentially the typical struc- 

 ture of the roots of the higher plants, and bear 

 no resemblance to those of the Lycopods. 



It may be added that tubers, serving to propa- 

 gate the plant, are borne, in some species, on the 

 underground branches of the stem. 



