THE AXATOMY OF WOOBY PLA>TS 59 



common origin with the cortex and so does not helong to the central 

 cyhnder. 



Much attention is given to the wood (especially the secondary 

 wood) as this is the tissvie for which the hest fossil evidence is avail- 

 able ; the libriform fibres are derived from tracheides, not from 

 ])arenchyma as Strasburger held. Evidence is given also for the 

 origin of xylem-parenchyma and of the so-called medullary rays from 

 tracheides, and some excellent new figures of Lepidodendroid structure 

 are furnished, in support of this view. The statement (p. 40 and 

 elsewhere) that tangential pits are absent in Palaeozoic woods is 

 erroneous ; they have long been described in Pitys antiqua and also 

 occur in Mrsojcylon multirame and doubtless in other species. In 

 Chap. vii. there is an excellent comparative account of xylem-vessels 

 in Gnetales and Angiosperms. The epidermis is said to be of "rela- 

 tively slight phylogenetic interest." Yet the stoma is probably the 

 most conservative organ of plants. 



The common term medullary rays is repeatedly condemned, on 

 the ground that their relation to the pith is only a "semblance," due 

 to obsolescence of the primary wood. This may he true, but the 

 relation is of very old date, for it was already well established in the 

 Calamites and some of the Cycadofiliees. From the author's point "of 

 view the wide ray is a compound one. derived from the aggregate type 

 of ray ; the vascular bundles were not originally separate, and the 

 statements of Sanio and Sachs as to the hridging over of the primary 

 gaps by interfascicular cambium are rejected. They are, however, 

 ti'ue, as a description of the facts, and hold good for the young 

 Calamite as well as for more modern plants. 



On the general question of the relation of herbaceous to arboreal 

 types, it may be pointed out that there is no proof that our existing 

 herbaceous Lycopods came from arboreal ancestors ; the herbaceous 

 ScJayinellites was contemporary with the arboreal Le]:)idodendreje. 

 'i'he siphonostele is held to have primitively possessed phloem on the 

 inner as well as the outer surface. This tv] e of structure, however, 

 is rare among Paheozoic plants. 



In the chapter on the micros])ora}igium the author adopts the view 

 that the higher plants arose from forms like the thallose Liverworts, 

 and quotes Power's Oriyiii of a Land Flora in support of this theory. 

 No mention is made of Prof. Bower's subsequent change of view. 



The " Canons of Compai-ative Anatomy " on which the author 

 insists are three in number — Pecapitulation, Conservative organs and 

 Jk>version. The doctrine of recapitulation in the development of the 

 individual of the histoi-y of the race is well known though no longer 

 accepted without question. The author points out that ncyative 

 evidence is of little or no value, but doubts may arise as to what 

 testimony is negative ; in a Pine-seedling for example, short-shoots 

 are absent, but foliage-leaves on the main stem are pi-esent. 



Among conservative organs the leaf is first cited, and tlicn the 

 ivjjroductive axis. The ])resent writer is given the credit for the 

 latter idea; it belongs rather to Solms-Laubach, but neither gene- 

 ralised the conclusion, which was confined to the })edmieles of Cyeads. 

 Floi'al axes are subject to modifications of their own, and are m)t 



