CELLS ОЕ EUCOMMIA ULMOIDES, OLIVER. 245 
on their transverse walls, as is the case in the primary phloem, and we find regular 
alternating peripheral rows of sieve tubes and companion cells, very often two of the 
former to one of the latter, as will be seen in fig. 14. Between the companion cells the 
cut ends of the caoutchouc threads will be seen. 
In the leaf a group of caoutchouc-containing cells accompanies the ramifying fibro- 
vascular bundles, running just below the phloem, while in the petiole and all along the 
bundle of the midrib they form two groups at the side of the bundle, and do not run 
below it. А few cells are scattered through the parenchyma, which forms the 
cushion on the underside of the midrib, and a good many are found in the parenchyma 
of the petiole. 
The pericarp of .Ewcommia, which resembles in appearance that of the Elm, is 
especially rich in these caoutchouc-containing cells. Below the epidermis of the peri- 
carp we find a few layers of large chlorophyll-containing cortical cells, which become 
very much compressed in the dry fruit. Within these are the fibro-vascular bundles, 
the main trunks running longitudinally, and connected by branching and anastomosing 
lesser bundles. The longitudinal bundles have a strong group of caoutchouc-containing 
cells accompanying them on their inner side, and immediately beneath them we find a 
large mass of circularly running cells of the same nature, forming quite a dense coat of 
hyphee-like thin-walled cells, showing their cell-walls very distinctly when the caout- 
chouc has been dissolved out by chloroform. 
Further within we find a group of thicker-walled cells very similar to and running in 
the same direction as the caoutchouc-containing cells, but with curious, almost black, 
granules and contents. The innermost layer of the pericarp consists of sclerenchy- 
matous cells. 
The caoutchouc-containing cells reminded me in many ways of the latex cells of the 
Euphorbiaceze and Аросупеге, in spite of their remaining unbranched and containing 
their caoutchouc in a consolidated mass. But the main difference between these cells 
and the latex cells became apparent when I began to study their development, and found 
that they can originate anew in all the secondary growths, both in the secondary phloem 
and also in all new organs, whether stem or leaf; whereas all true latex cells, according 
to Chauveaud’s latest embryonic researches *, arise from a limited number of initial 
cells, which can be distinguished at an early stage in the development of the embryos 
of Euphorbiacez, Urticaces, Apocyne, and Asclepiade. 
Schmalhausen +, it is true, had previously affirmed this embryonic origin of latex cells 
for a large number of cases, but his observations did not include the latex cells which are 
found in the secondary phloem in Ficus, Morus, Broussonetia, Maclura, and Nerium. 
These, however, according to Chauveaud, are also formed from the specialized cells of 
the embryo mentioned above, for, as he says (p. 151) :— ; 
* Dans les cas ой la plante acquiert des formations secondaires, ces formations sont 
parcourues par des tubes laticiféres issus des branches voisines des assises génératrices 
* Chauveaud, G., in Annales des Sciences naturelles, série vii. tome xiy. (1891) pp. 1-160. 
+ Schmalhausen, in Меп, de Асай. de St. Pétersbourg, 7° série, vol. xxiv. (1877) no. 2. 
2x2 
