On Caoutchouc in Plants. 
27 
of species of Hippocrateaceae and in Plagiopteron these cells attain 
so great a length, that 1 have rarely observed a termination in 
those which traverse the stem ; nor do transverse partitions occur 
in their course. In the case of Hippocratea ovata Lam. it has been 
possible to show that these caoutchouc-cells are present in the 
embryo in the seed, where they occur very abundantly in the 
cotyledons. Hence they are comparable to the latex-elements of 
Moraceae, Apocynaceae, etc.; a similar eariy development is 
probable for the other species. 1 
They are present in both primary and secondary phloem of the 
stem, as well as in the primary cortex ; in Plagiopteron alone they 
are found in the pith. While very common in phloem and cortex of 
the petiole, in the leaf they are restricted to the under-side of the 
veins, where they usually replace part or all of the sclerenchyma, 
accompanying the vascular bundle. Here however branching, which 
is very rare in other portions of the plant, is of common occurrence 
in some species. The branches originate from the laticiferous 
elements, accompanying the vascular bundles, and ramify freely in 
the spongy tissue; only rarely do they pass into the palisade- 
parenchyma. Caoutchouc-cells occur throughout all parts of the 
flower, penetrating alike into sepals, petals, stamens and style. 
Laticiferous elements of this type, extending throughout all the 
organs of the plant, are found in all species of Witnmeria, in 
Plagiopteron and in a number of the Hippocrateaceae. Other 
members of this latter order however have caoutchouc-cells of a 
different type, also occuring in Evonymus and other genera of the 
Celastraceae proper. 1 In these cases no laticiferous elements are to 
he found in young branches, although those of some years’ growth 
are often very rich in them; thus a stem of Salacia Roxburghii, 
measuring about 1 cm. across, is devoid of these structures, 
whereas one of about cm. diameter was found to contain them very 
abundantly in the secondary portion of the rind Apparently the 
stage at which they begin to appear, is arrived at earlier in the 
growth of some species, than in that of others, so that it is quite 
possible that the list of caoutchouc-containing species will be con¬ 
siderably increased when opportunities for the examination of 
thicker stems are afforded. Some species of Hippocrateaceae 
however certainly never possess caoutchouc, 2 since it is wanting in 
1 It is no easy matter to obtain the fruits of species of Hippo¬ 
crateaceae, so that an investigation of the seed has only 
rarely been possible. As for Plagiopteron, although 1 have 
examined a number of fruits, they were always devoid of 
seeds, the ovules having apparently aborted 
