GROUP III. PTEKIDOPHYTA : EQUISETINjE. 



417 



B 



generally green in colour, and their surface is more or less strongly ribbed. 

 Some of these shoots are sterile, whilst others are fertile, bearing the sporangia. 

 In most species the sterile and fertile shoots are alike (Equiseta homophyadica), 

 but in the four species E. arvense, maximum, silvaticum, pratense (Equiseta 

 heterophyadica) they are more or less widely different. Thus in E. arvense 

 and maximum, the fertile shoots are developed early in the spring, and are un- 

 branched, whereas the copiously branched sterile shoots are not developed till 

 the summer; moreover the fertile shoots are not green. In E. pratense the 

 diffetences between the fertile and sterile shoots is less marked, the former bear- 

 ing a few whorls of simple 

 branches. InE. silvaticum 

 the fertile shoot has no 

 branches at first, but after 

 the shedding of the spores 

 the terminal cone dies off, 

 the shoot throws out 

 branches, and thus comes 

 to be a sterile shoot. In 

 some species the sub-aerial 

 shoots are generally un- 

 branched (e.g. E. hiemale, 

 trachyodcn, variegatum). 



The leaves are either cu- 

 taphylls or sporophylls. The 

 cataphylls, representing the 

 foliage-leaves, are borne in 

 whorls at the nodes, having 

 a common attachment, so 

 that they form a leaf-sheath 

 at each node. They are 

 small and brown in colour. 



The sporophylls, like the 

 cataphylls, are developed in 

 whorls, but owing to the 

 fact that the internodes 



k 



between the whorls do not 

 elongate, the sporophylls 

 are aggregated into a cone- 

 like flower situated termin- 

 ally on the shoot (Fig. 272), 

 or less commonly (>'.g. E. 

 palastre) on some of the 

 lateral branches. The leaf- 



Fia. 272. A Upper portion of a fertile branch of 

 Equisetum palustre. v Leaf-sheaths, below which the 

 branches (r) spring; 10 the uppermost sterile she ah 

 (ring) ; a the flower ; s the peltate sporophylls. B Trans- 

 verse section of the stem (x 6): c central cavity; s the 

 vascular bundles arranged in a circle, each having 

 a carinal cavity, It; f the vallecular cavities; r the 

 ridges. C Sporophyll with sporangia ( x 10) : st the 

 stalk; sp the sporangia. D Diagram of the course 

 taken by the vascular bundles where two internodeB 

 meet ; ti the internodes ; fc the node. 



sheath below the cone, 



marking off the reproductive from the vegetative region of the shoot, is peculiar, 



being generally very much reduced, and is termed the ring (see p. 79). 



Each sporophyll has a small hexagonal lamina which is inserted on the axis 

 of the cone by a short stalk attached to the centre of the inner surface of the 



V. s. B. 



E E 



