ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 771 



continued indefinitely from the cotyledons into the stem and leaves, 

 in the pericycle, more or less near to the liber of the vascular bundles, 

 but not in the liber itself. The same is also the case in the Pitto- 

 sporese. In the root of Liguliflorse (Compositse) the laticiferous 

 network occupies the internal edge of the liber within the sieve- 

 tubes, while in the stem it is situated in the pericycle outside the 

 sieve-tubes. In those Tubuliflorfe which possess a secreting system, 

 its position in the roots is the same as in the Liguliflorae. The root 

 of the Radiatse and Liguliflorfe is altogether destitute both of a 

 laticiferous network and of isolated resiniferous cells, although 

 possessing an endodermic oleiferous system. 



In the Clusiaceas the only regions in which secreting canals are 

 not found are the pericycle, which forms in the stem a sclerenchy- 

 matous ring, aud the primary or secondary xylem of the vascular 

 bundles. The Hypericaceas resemble the Clusiaceas in the constant 

 presence of secreting canals and in their general disposition, but 

 differ from that order in their presence in the pericycle. The 

 Ternstroemiaceae present in this respect a close resemblance to the 

 ClusiaceEe. The DipterocarpeaB differ, not only from these orders, 

 but from all other angiosperms, in the presence of secreting canals in 

 the xylem. In the complicated arrangement of the vascular bundles 

 in the petiole they approach Malvaceae. 



Liqiddambar and Altingia have their entire vegetative structure 

 traversed by a system of oleiferous canals belonging to the primary 

 liber in the roots, to the primary xylem in the stem and leaves. They 

 may be said to combine the root of Anacardiaceaa with the stem and 

 leaves of Dipterocarpeaa. The Simarubete have canals only in the stem 

 and leaves, not in the root. The Dipterocarpeas, Liq^uidambareas, 

 and Simarubeffi have this in common, that the stem and leaves have 

 secreting canals localized in the primary xylem ; they are dis- 

 tinguished from one another by the position of the canals in the 

 root ; in the DipterocarpeaB these are in the primary xylem, in the 

 LiquidambareaB in the primary liber ; in the Simarubeae there are 

 none. In tlie only other order which has secreting canals in the 

 xylem, the Coniferae, they occur only in the root and stem. 



Anatomical Structure of the Root.* — J. Constantin points out the 

 great uniformity in the structure of the root as compared with that of 

 the stem in the great divisions of the vegetable kingdom ; but this ho 

 attributes to the much greater uniformity in the nature of the en- 

 vironment. In differing external circumstances he finds the structure 

 of the root to vary in precisely the same directions as that of the stem. 



When a root is fully exposed to the action of light, the thickness 

 of the bark is less than in an underground root, while the central 

 cylinder is, on the other hand, more developed. The endodermic 

 punctations, so clear in underground roots, become indistinct in roots 

 exposed to the light ; all the fibrous tissues are more developed, both 

 in the central cylinder and in the bark ; and lignification has advanced 

 considerably further. 



♦ Bull. Soc. Bof. France, xxxi. (1881) pp. 25-8. 



