ANATOMY" AND I'll V LOGENY OF THE CONIPERALES. 



T.) 



Persistent as ancestral characters are in the reproductive axis, they are much 

 more markedly so in the foliar organs. In the case of the Cycads, the fibrovascular 

 bundles of the leaves are of the old quasi-cryptogamic mesarch type found in the 

 medullary crown of the vegetative stem of Lyginodendron and others of the transitional 

 Gymnosperms. We thus find living on in the leaf, a type of bundle which in the 

 Cycads has long disappeared in the vegetative stem and occurs only in rare; instances 

 even in the more conservative reproductive axis (Scott, '97) . A similar feature is 

 presented by the leaf bundles of Lyginodendreae (Williamson and Scott, '95) and the 

 Osmundaceae (Faull, :01; Jeffrey, : 02) , for in these groups the concentric Filicinean 

 type of fibrovascular strand, which has almost disappeared in the fibrovascular zone 

 of the stem, persists, often in full vigor, in the leaves. It has further been shown by 

 Jackson ('99) that the outward form of the earlier or nepionic leaves of many Angio- 

 spermous and Coniferous seedlings presents striking resemblances to the adult leaves 

 of extinct fossil species. Numerous other examples and illustrations of the same 

 principle might be cited, but the foregoing have been chosen because they are 

 particularly convincing on account of their confirmation by fossil data. 



Lastly, in this connection we come to the ancestral features presented by the 

 seedling. It is a recognized principle in the embryology of animals that ancestral 

 features are apt to persist in the earlier stages even where they have quite dis- 

 appeared in the adult. As a striking illustration of this principle may be cited 

 the fact that gill slits are found in the embryos of all the great groups of the Ver- 

 tebrata, although gills have long disappeared in the adult of most of the classes 

 of the phylum. In the case of plants, as has been pointed out by Scott ('96), 

 this feature is much less marked, but striking examples of recapitulation in the 

 case of seedlings have been described by Strasburger (72) , Goebel ('89, date of part) , 

 Jackson, and others. The Cupressineae present particularly good illustrations of this 

 principle, since in them the older stem has undergone very marked xerophytic modi- 

 fications in the way of flattened, appressed leaves, etc. These extreme xerophytic fea- 

 tures are absent as a rule in the seedling, where a somewhat Taxodineous type of 

 foliage is often found. The more ancestral type of foliage may further be discov- 

 ered in the relatively more vigorous main axes, where there is often present a 

 larger and less appressed type of leaf. In this connection may be mentioned the 

 reversion to ancestral conditions of internal structure, which sometimes occurs in the 

 first annual ring of vigorous branches. The writer has pointed out in the first 

 memoir of this series (Jeffrey, :03) that in the more vigorous ramifications of the 

 cone-bearing shoots of Sequoia gigantea there occur, in the first annual ring only, 

 resin canals such as are found as an unfailing structural feature of the wood in 



