244 MR. Е. E. WEISS ON THE CAOUTCHOUC-CONTAINING 
The threads of Еисоттіа consist therefore of caoutchouc, for they are insoluble in 
alcohol, acids, and alkalis, though they become soft when treated with ammonia. "They 
dissolve in chloroform and turpentine, and swell up in ether. When heated they melt, 
and they burn with the characteristic smell of burning rubber. 
It is still uncertain whether the many substances described as caoutchouc or india- 
rubber are always the same chemical body, but that these threads consist of a substance 
having the usual characteristics of caoutchouc is beyond doubt. 
With certain colouring reagents these threads were, curiously enough, stained in the 
same manner and of the same colour as the cuticle covering the epidermal cells. Thus 
when treated with dilute iodine they rapidly assume a dark yellow or brown colour, 
while the remainder of the section is only faintly stained. Similarly, methyl green 
acidulated with acetic acid stains both the cuticle and the caoutchouc threads intensely 
violet, while the rest of the section is stained light green, the xylem vessels being some- 
what darker, but not of a violet colour. 
From the bark the rubber can very readily be extracted. If the bark be broken in 
pieces and pounded in a mortar, the mass can be roughly separated into two parts—one 
consisting of the tangled elastie threads, with small bits of broken bark adhering to 
them, the other chiefly of bits of bark containing, no doubt, smaller pieces of the threads. 
From both parts chloroform will dissolve out caoutchouc, а larger amount naturally 
from the portion which consists chiefly of the threads. Thus a sample of the threads 
and bark weighing 443 mg. gave as much as 25 mg. of caoutchouc, while the remaining 
bark, weighing 607 mg., yielded only 6 mg. Taking the two quantities together, the 
yield of caoutchouc was З per cent. of the weight of the dry bark, and the same figure 
was arrived at independently by Professor F. W. Oliver with another sample. 
The threads are clear and homogeneous, and the only impurity in the chloroform 
extract seems to be a little resin, which can be washed out with alcohol. 
Whether the bark can be made use of commercially I must leave to those who are 
more experienced in technical matters, but it is interesting to note that efforts are now 
being made to extract gutta-percha from the bark of trees which have been drained in 
the ordinary way of that product. Тһе yield in these cases was 5:3 to 5'7 per cent. of 
the wet bark used.* 
The threads themselves in situ in a section, both in longitudinal and transverse aspects, 
are highly doubly refractive, and remain so when swelled up with ether; but they lose 
this optical property when dissolved in turpentine or melted into an amorphous mass. 
The distribution of the caoutchouc-containing cells I had been able to determine from 
the dry material which I first examined, and these observations were confirmed by the 
examination of the material preserved in alcohol. They occur in the inner portions of 
the cortex, very much in the position in which the latex cells of Euphorbia are found, 
but are even more frequent in the secondary phloem, where they run between the 
companion cells (figs. 14 & 15), and in both cases present the appearance of very long 
narrow cells, attaining such a length that one only occasionally finds their ends. The 
sieve tubes of the secondary phloem have their sieve plates on their lateral radial, not 
* Bulletin of Miscell. Information, Kew, September 1891. 
