FUNCTIONS OF LATEX-TUBES 341 



biglandulosa. In these species the parenchymatous sheaths of the 

 smaller vascular bundles are interrupted at numerous points, while the 

 individual cells are not of the normal elongated type, but often appear 

 as broad as they are long, and generally present an irregular outline. 

 In the mid-ribs the ordinarily massive conducting parenchyma is almost 

 entirely suppressed, its place apparently being taken by from six to 

 eight wide latex-tubes, which in places lie in immediate contact with the 

 leptome. To what extent the vicarious activity of the laticiferous 

 system may affect the development of the leptome itself, is uncertain. 

 De Bary goes so far as to maintain that the sieve-tubes of many 

 laticiferous plants (e.g. the Asclepiadaceae) are unusually narrow and 

 inconspicuous ; Kniep, however, disagrees with this statement, at any 

 rate so far as stems are concerned. 



Anatomical evidence alone cannot, of course, supply a convincing 

 proof of the importance of the laticiferous system in connection with 

 the translocation of plastic materials. As a matter of fact, all 

 attempts to reach a definite conclusion regarding this point along 

 experimental lines have also so far met with indifferent success. 

 In most of the experiments in question, the method employed 

 has been that of determining the composition of the latex, either 

 at different points of the life-history of the plant, or else under 

 normal and abnormal external conditions ; from the data obtained 

 in this manner, conclusions have been drawn as to the nutritive 

 value of the latex. 



The variations in the composition of latex which are correlated with 

 different stages of development of one and the same species, have been 

 investigated in detail in the case of Euphorbia Lathyris by Schullerus. 

 In the developing embryo the latex contains a large amount of starch, 

 oil, protein compounds and tannin. When the embryo enters upon its 

 period of rest, in the ripe seed, the latex has become transparent, and 

 contains a much smaller proportion of plastic materials, the starch- 

 grains having disappeared altogether, while both oil and tannin are 

 present only in small quantities. During the germination of the seed 

 the latex again becomes viscid and full of suspended particles ; the rod- 

 shaped starch-grains reappear in large numbers, and the rest of the 

 above-mentioned plastic substances once more show a decided increase. 

 In the adult plant the latex retains this viscous consistency and 

 nutritious character throughout the vegetative season. During the 

 resting period that is in winter time its quality again deteriorates. 

 At this time it is characterised -so far as the stem is concerned 

 by the small amount of plastic material which it contains, and by the 

 appearance of a fresh constituent in the form of calcium malate ; in the 

 roots the amount of protein in the latex actually increases during this 



