CONIFERALES (TAXACEAE) 315 



and Polypodiopsis (i species, in New Caledonia). The New Cale- 

 donian representation is so small, and the affinities of Polypodiopsis 

 are so uncertain, that the tribe may be regarded as northern in its 

 distribution, in contrast with the southern distribution of the podo- 

 carps. The difficulty of estimating the number of species may be 

 illustrated by Taxus, at least 75 species of which have been described, 

 7 of which are recognized by Benthaj^i and Hooker; and these have 

 been reduced to a single species by Pilger (81). 



The Taxaceae and Pinaceae have so many features in common 

 that in the following account, to avoid needless repetition, attention 

 will be called chiefly to the differences. 



I. The vegetative organs 



The general habit of the body of Taxaceae resembles that of Pina- 

 ceae. In some forms, also, the branches are dimorphic, the dwarf 

 shoots of PhyUocladus being transformed into the characteristic 

 phylloclads (fig. 373). The phylloclads are in the axils of small 

 scalelike leaves, which are at first green, but later become true scales, 

 and are really developed by the primordia of foliage leaves; while 

 in the juvenile forms the first leaves are flat green needles, which are 

 successively replaced by shorter and shorter ones until the adult form 

 is reached, and the phylloclads themselves only gradually acquire 

 their peculiar character (fig. 256, e, /). It seems evident that this 

 peculiar form has been derived from forms with ordinary spreading 

 needles and axillary dwarf shoots. 



VASCULAR ANATOMY 



The structure of the stem is the same as that of Pinaceae, the 

 vascular cylinder being collateral endarch. Among the taxads, 

 however, the traces of ancient structure in the form of mesarch bundles 

 are of more general occurrence than in any other tribe of conifers. 

 Pronounced mesarch bundles occur in the cotyledonary strands of 

 Cephalotaxus (45, no, 141), and less obviously in those of Taxus 

 (no, 141) and Torreya (75); while one species of Cephalotaxus 

 is reported to have a mesarch stem cylinder. Among the podocarps 

 mesarch bundles occur in the phylloclads of PhyUocladus (115), 

 and there are apparently traces of centripetal xylem in the axis of 



