96 STRUCTURAL BOTANY 



The roots of Equisetum branch freely ; the origin of 

 the branches, as in other roots, is deep-seated or endo- 

 genous. In this case it is from the inner layer of the 

 double endodermis that the rootlets are formed, each of 

 them arising from a single cell which lies just on one 

 side of a protoxylem-group. This cell divides up so as 

 to form an apical cell of the usual pyramidal form. The 

 rootlet has to make its way through the whole thickness 

 of the cortex, and in doing so is helped by the presence 

 of a digestive sac (see Part I. p. 171), formed from 

 the outer endodermal layer, which thus constitutes a 

 temporary covering to the young root. 



Y 



2. BEPRODUCTIVE ORGANS OF THE SPOROPHYTE 



We have already learnt the main points in the 

 structure of a cone of Equisetum so far as they can be 

 seen with the naked eye or a pocket lens (see p. 82). 

 It remains for us to make ourselves acquainted with the 

 more minute characters. The anatomy of the axis of 

 the cone is in all essentials just the same as that of a 

 vegetative stem, and the development takes place in the 

 same manner, though the growth of the cone is limited. 

 The whorls of sporangiophores are in origin somewhat 

 similar to the whorls of vegetative leaves, but in the 

 fertile cone scarcely any sheath is developed, so the 

 sporangiophores are separate outgrowths almost from the 

 first. The upper part of the sporangiophore soon begins 

 to grow in diameter more rapidly than its base, which 

 thus becomes constricted, so that the mature peltate form 

 is already indicated. At about the same time the spor- 

 angia begin to show themselves as slight outgrowths pro- 

 jecting from the under-side of the expanded portion. Each 



