LATICIFEROUS VESSELS OF HETEA. 569 



endosperm, through the cotyledons, to the developing organs of 

 the embryo # . From this point of view its early development is 

 quite intelligible, while the relatively backward condition of the 

 xylem is explained by the fact that no demands can be made 

 upon its function as water-conducting tissue until the roots are 

 able to take up water from the soil. 



At a much later stage of germination the development of the 

 xylem was still fouud to have gone on but slowly. Thus in the 

 main root, when it has attained a length of nearly 4 centims., 

 scarcely "-any of the vessels are differentiated at a distance of 

 2 centim. from the apex, while in the hypocotyledonary stem and 

 epicotyledonary internode of similar seedlings, the xylem, though 

 more advanced, is still backward compared to the laticiferous 

 tissue. As regards other elements of the bundles, the sieve- 

 tubes appear at a relatively early stage. These organs are well 

 developed, both in H. brasiliensis and H. Spruceana ; so that in 

 this genus, as in Manihot, we find no signs of that reduction of 

 the sieve-tubes which is supposed to characterize plants with 

 abundant laticiferous tissue f. 



The laticiferous vessels cannot be traced into the apical cone 

 above the youngest leaves. This is' what would be expected from 

 their relation to the leaf-trace bundles. I found this to be also 

 the case with the laticiferous vessels of the Cichoraceae +. 



To my observations on Hevea Spruceana, I have not much to 

 add. Figs. 3 and 4 show laticiferous vessels from the phloem in 

 tangential and radial section respectively. In fig. 3 the charac- 

 teristic lateral anastomoses are conspicuous, and at t the remains 

 of a transverse wall are visible. There is no doubt that here, as 

 in Manihot, transverse walls are present at first, which in most 

 cases afterwards entirely disappear. The oblique walls with 

 numerous perforations, described in my note in the ' Quarterly 

 Journal ' as terminal, are in reality portions of the lateral walls, 

 owing their oblique position to the curved course of the vessels 

 where they pass round the ends of the medullary rays. As stated 

 above, all the more important observations as to structure and 

 development of the tissue in question may be taken, ■mutatis 

 mutandis, as applying to both the species alike. 



* Cf. Haberlandt, Physiologische Pflanzen-Anatomie, 1884, p. 227. 

 t For the prevalent views on this point cf. DeBary, Comparative Anatomy, 

 translation, pp. 432 and 525. 



\ Quarterly Journal Micr. Sci. 1882. 



