PTERIDOPHYTA— LYCOPODIN^ 155 



Class VIII.— LYCOPODIN^. 



Like the Filicinse, this class embraces both isosporous and 

 heterosporous forms, and is divided accordingly. The plant is 

 the sporophyte, and aU the plants of the class are eiisporangiate. 

 Though of a somewhat higher type than the Ferns and Horse- 

 tails with regard to then processes of reproduction, their vegeta- 

 tive body is usually not so conspicuous, though in this respect 

 there is a great deal of variety. The development of the embryo 

 from the zygote, so far as it has been followed in the group, is 

 much more like the process found in the flowering plants. The 

 foot^ so prominent in the embryo of the Ferns, is replaced by a 

 cell or filament of cells known as a suspe7isor, and a special 

 absorbing structure is developed from the epibasal portion of 

 the embr^'o, which is often erroneously spoken of as a foot. 

 It functions in the same way as a true foot, but is developed 

 from an altogether different part of the embryo. We have, 

 mdeed, in the action of the foot in the Ferns and of this new 

 organ in the Lycopodinae an instance of the same physiological 

 function bemg discharged by different morphological members. 



Section 1. — Isosporous Lycopodin^. 



Included in this section are two Natural orders, Lycopodiaceae 

 and Psilotaceae, each of which comprises two genera, Lycopodium 

 and Phylloglossum, Psilotum and Tmesipteris. 



Lycopodium is much the largest genus, comprising many 

 species of very varying external appearance. Generally there is a 

 very much-branched wiry stem, sometimes growing miderground, 

 sometimes creeping on the surface, sometimes erect. It is 

 closely covered with variously arranged small, pointed leaves, 

 which are very numerous. The stem sometimes branches dicho- 

 tomously, sometimes monopodially. 



Besides the foliage leaves the plant bears sporophylls, which 

 are often very different in appearance from the former, and are 

 collected into flowers at the end of the branches. The flowers 

 are cones, consisting of spirally arranged leaves bearing the 

 sporangia in their axils or on the upper surface of the leaf- stalk 

 {fig. 916). In some species the collection of the sporophylls mto 

 cones is not so obvious, and then the sporophylls closely resemble 

 the foliage leaves. The roots are all adventitious, and in many 

 cases arise from superficial cells of the stem. 



