HOLLOWAY. — Studies in the New Zealand SjJecies of Lj-copodium. 211 



that the mature form and structure of the plant is a more or less recent 

 modification. In the young plant the habit is orthotropic for a lengthy 

 stage. The stimulation of the cortical and stelar tissues to an increase in 

 girth does not take place till after the stem has begun to assume the 

 plagiotropic habit, and is then localized in its terminal region. This indi- 

 cates that the character of unlimited growth from a broad apex has been 

 an added feature in the phylogeny. The character of heterophylly makes 

 a somewhat earlier appearance, though not so early in the sporeling of 

 L. volubile as in that of L. scariosum. The stelar anatomy of the stem is 

 primarily radial, as in the Selago and Phlegmaria sections, but this becomes 

 )nodified to a characteristic dorsiventral arrangement by the restriction of 

 the branching of the mature stem to one plane. The large size of the stele 

 and the differentiation of the xylera and phloem into large conducting 

 elements and flanking storage elements has come about simply through the 

 extended growth of the plant, this being most marked in the scrambling 

 stem of L. volubile. The subterranean habit of the main stems of L. densum 

 and L. fasfigiatum is an extreme modification and is only found in a few of 

 the species. In some species — for example, L. densnni — the cones are very 

 numerous, every terminal branchlet in the upper portion of the erect aerial 

 shoot being fertile. In this case the cones are quite short and are not 

 always erect, and there is no suggestion of a pedicel. In other species — for 

 example, L. scariosum. and L. fastigiatum, — there is a great restriction in the 

 cone-formation, only the main branchlets being fertile. The cones are here 

 long and club-shaped, and are raised on long pedicels through the continued 

 growth of the axes of the branchlets. Moreover, the pedicels sometimes 

 branch, and also sometimes even the cones themselves. This club-shaped 

 condition of the fertile region must be considered the most modified form 

 of strobilus in the plagiotropic species of Lycopodium, except that the 

 pendulous strobili of L. volubile are an extreme modification. That the 

 club-shaped cone is not a phylogenetic feature, but an adaptation only, 

 seems to be indicated by the fact that in L. fasfigiatum both the densum 

 condition and the scariosum condition occur in a most marked degree. 



The prothallus shows two main types which are adapted to a sub- 

 terranean mode of life. It is noteworthy that whereas in L. tSelago the form 

 of prothallus which grows deepest is the branched form, while the compact 

 massive form occurs at the surface, and also that in L. Billardieri, &c., 

 the subterranean habit has resulted in a much-branched structure, in the 

 species of the Clavata section the subterranean habit goes along with two 

 types of prothallus, both of which show the compact and massive form in a 

 most marked degree. The branching which occurs in the young prothallus of 

 L. fastigiatum may be significant in this respect, as indicating that this type 

 has not altogether lost the disposition to branch. In fact, in all the New 

 Zealand species the form of the prothallus is not invariable, L. volubile 

 and L. fastigiatum showing a lobing of the upper surface, and a pseudo- 

 branching being found in some large individuals of L. scariosum (16). 

 Bruchmann (5, 6) has shown also that the lip of the prothallus of 

 L. annotinum may grow out into long frill-like protuberances, and that the 

 prothallus of L. comjAanatum may bud. All these features, however, 

 possibly have no phylogenetic significance at all, but are recent modifica- 

 tions. The prothalli of both the Phlegmaria and the Clavata sections have 

 adapted themselves to a subterranean habit, and have departed from the 

 chlorophyll condition, although the clavatum. type has done this to a less 

 extent than has the comjilanatum type. As regards the dift'erentiation of the 



