THE VASCULAR CRYPTOGAMS 83 



numerous spores, which are all of one kind. At the 

 bottom of the whole cone is a ring of abortive leaves, 

 called the annulus (see Fig. 38, 1, a); sometimes there 

 are two such rings. These rudimentary structures are 

 of some interest, because in many of the fossil forms 

 there are whorls of barren leaves or bracts between the 

 whorls of sporangiophores. It is possible that we find 

 the last remnants of these bracts in the annulus of living 

 Horsetails. 



II. INTERNAL STRUCTURE AND DEVELOPMENT OF 

 THE SPOROPHYTE 



1. VEGETATIVE ORGANS 



a. The Stem 



The general structure of the stem in the genus 

 Equisetum is at once simple and characteristic. Among 

 all the Cryptogams now living, these plants approach 

 most nearly, as regards their anatomy, and especially 

 that of the stem, to the simpler Gymnosperms and 

 Dicotyledons, though in other respects they differ widely 

 from them. The stem of Equisetum is invariably 

 traversed by a number of collateral leaf-trace bundles, 

 arranged in a single circle. The course of these bundles 

 is excessively simple ; a single one enters the stem from 

 each leaf, i.e. from each tooth of the coherent sheath. 

 It passes straight down the whole length of the internode, 

 without joining on to any other bundle until it reaches 

 the node below. Here it forks into two, and the forks 

 attach themselves to the two adjoining bundles coming up 

 from below, just where they are beginning to bend out into 



