GROUP III. PTERIDOPHYTA: 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 



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

 ing a few whorls of simple 



branches. In E. 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, 



trachyodon, variegatum). 

 The leaves are either ca- 



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 interaodes Flfc 272 _ A Upper portion of a fertile branch of 



between the whorls do not Equisetum palustre. v Leaf-sheaths, below which the 

 branches (r) spring; tc the uppermost sterile sheath 

 (ring) ; a the flower ; g 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, fc ; / the vallecular cavities ; f 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 internodes 

 meet ; ii the internodes ; i the node. 



elongate, the sporophylls 

 are aggregated into a cone- 

 like flower situated termin- 

 ally on the shoot (Fig. 272), 

 or less commonly (e.g* E. 

 palustre) on some of the 

 lateral branches. The leaf- 



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 



