xii EQUISETINEJE 457 



characteristic rhizomes. The "first of these have also four- 

 toothed sheaths, but the branches produced from them gradually 

 assume the characters of the fully-developed shoots, some of 

 which ultimately bear sporangia. The first shoots of the sporo- 

 phyte, even in such species as later branch very freely, produce 

 only an occasional branch, which breaks through the base of the 

 sheath. 



In E. hiemale, there is found, according to Jeffrey, a gradual 

 transition from the typical arrangement of the tissues of the 

 root, to those in the base of the young shoot. There is first 

 developed in the latter an unbroken tube of reticulate tracheids, 

 which Jeffrey considers to be a reversion to an originally cylin- 

 drical stele. However, as this same arrangement is repeated 

 in the succeeding nodes, it seems much more likely that this 

 ring of tracheary tissue merely represents the basal node. 

 Within the ring of tracheary tissue is a mass of parenchyma, 

 and outside a zone of phloem bounded by a typical endodermis. 

 The rudiment of the second shoot causes a break in the vascular 

 ring above its point of origin. In the internode there are three 

 vascular strands, corresponding to the three teeth of the foliar- 

 whorl. In short, the structure of the primary shoot is essen- 

 tially the same as that of the stouter shoots developed subse- 

 quently. Although Jeffrey speaks of a "central-cylinder," there 

 is nothing in his account to show that the vascular bundles do 

 not originate from the primary cortical tissue, as they do in the 

 adult shoots. 



THE MATURE SPOROPHYTE 



On comparing the sporophyte of Equisetum with that of 

 most Ferns, the greatest contrast is in the relative importance 

 of stem and leaves. The stem in all the Equisetineae is extra- 

 ordinarily developed, while the leaves are rudimentary, in strong 

 contrast to their great size and complexity in most Ferns. All 

 species of Equisetum produce a more or less developed under- 

 ground rhizome, which often grows to a great length and rami- 

 fies extensively. This, like the aerial branches developed from 

 it, shows a regular series of nodes and internodes. The latter 

 are marked by longitudinal furrows, and about each node is a 

 sheath whose summit is continued into a number of teeth, vary- 

 ing with the size of the stem. Corresponding to each tooth 



