SECT. xi. SELAGINELLA. 375 



clothed with distichous leaves ; but sometimes it is tall 

 and erect, having feathery branches clad with leaves. 

 The sporangia are sacs, with two or three valves con- 

 taining large spores and sub-globose antheridia, con- 

 taining orange-coloured or minute scarlet bodies, ulti- 

 mately developed into spermatozoids. The species are 

 very numerous and greatly varied, and mostly tropical. 



From a comparison of the structure of the stems 

 of the fossil plants, Sigillaria and Lepidodendron, 

 Dr. Hooker concludes that they are highly developed 

 Lycopods, approaching closely in structure to the highest 

 class of plants. The stems of the former differ chiefly in 

 size from those of the Lycopodium, and the cones of 

 the Lepidostrobus differ in their greater development 

 and in the thickness of their scales from those of the 

 Conifers. The spores of the Lepidostrobus ornatus too 

 are sphericotetrahedral, like those of the Lycopodium. 

 But inferior as the existing Lycopods are to their fossil 

 ancestors, their analogy to the Conifers gives them 

 a more exalted position in the vegetable world than 

 their tall and graceful allies, ' the tree ferns.' 



The gradual change of structure from the lowest to 

 the highest cryptogamic form is accompanied by a 

 singular variety in the mode of reproduction, and a 

 degree of vital energy scarcely to be expected, at least 

 in beings of such low organization as the yeast plant, 

 which produces gemmae in vast and rapid profusion, 

 each gem or bud being only a facsimile of the parent 

 cell. In like manner the mother plant is reproduced 

 by the germination of the green zoospores, the green 

 globular cells in the fronds of the lichens, the motile 

 gonidia, and the discs in the baskets of the Marchantia, 

 especially those of the Marchantia polymorpha, which 

 have such vigorous vegetation that they form stomates 

 on whichever side is turned to the light, and roots on 

 the other. The result of all these is an individual 



