2] THE VARIOUS GROUPS OF PLANTS 57 



worts, unbranched and extremely short ; these last, peculiar types, 

 also have relatively large, elongated leaves. In them and some other 

 members, the leaf has a characteristic tongue-like appendage (ligule) 

 near its base. Fig. i6, showing examples of some types from this 

 group, indicates the range of existing forms. These are the main, 

 sporophytic plants, and they produce spores in sporangia borne 

 singly in the axils of special and usually modified leaves (sporophylls) 

 that either occur in groups at intervals along the stem or, more 

 often, form terminal cones. In some types the spores are all of 

 one kind, but, in others, different sporangia produce numerous 

 small ' microspores ' or relatively few (occasionally one) large 

 ' megaspores '. 



On germination the spores produce prothalli, representing the 

 gametophyte generation. These are always small and relatively 

 obscure bodies. However, they vary in different types from lobed 

 photosynthetic ones or underground non-green tuberous ones living 

 saprophytically with the aid of mycorrhizas (in either case usually 

 producing both male and female organs on the same prothallus), to 

 limited growths largely enclosed within the old spore-wall in those 

 instances where spores of two different sizes occur. In such instances 

 the megaspores each produce a few female organs and the tinv 

 microspores only a single male organ, the ' prothalli ' being dependent 

 upon the food stored earlier in the spore by the sporophyte. Follow- 

 ing fertilization by the spirally-shaped, swimming s^ermatozoid, the 

 egg develops in situ into a new sporophvte plant which is photo- 

 synthetic and independent from an early stage, so reversing the 

 situation met in Bryophyta. Some Club-mosses produce bulbils or 

 gemmae which are effective in multiplying the sporophyte. More- 

 over, vegetative propagation following fragmentation of large old 

 plants often occurs, at least among the longer trailing types. 



The Lycopodineae are fairly numerous in species and wide in their 

 habitat tolerance. Though most characteristic of shady woods from 

 tropical to boreal regions, or, in the case of Quillworts, of the beds 

 of freshwater lakes, they also occur in more exposed heaths and 

 marshes and, in such situations, range far north in the Arctic. 

 Nevertheless, as components of vegetation, except very locally and 

 then usually far beneath the dominants, or occasionally in deserts 

 where little else grows, they are so very minor as to be almost 

 negligible. Very different was the position of some of their fossil 

 relatives, which, as we shall see in Chapter V, apparently dominated 

 whole forests in much earlier geological ages, and greatly contributed 



