Notes . 
179 
become alternate. In some points Plagiopteron seems to form a 
connecting link between Elaeocarpaceae and holopetalous Tiliaceae, 
but in others it appears to stand quite alone. 
One of these, which is at the same time the most interesting feature 
of the plant, is the occurrence of caoutchouc-cells throughout its 
tissues. If any part of a dried specimen be broken into two halves 
and these carefully drawn apart from one another, large numbers of 
elastic threads of a whitish colour are seen to stretch between the 
two pieces, breaking off when they have been separated to a certain 
extent. Griffith mentions this phenomenon, saying (loc. cit. p. 246) 
that the plant ‘abounds with spiral vessels.’ The true nature of 
these threads was first determined by Radlkofer 1 , who mentions 
their occurrence in Plagiopteron , whilst describing Wimmeria cyclocar pa, 
which is provided with similar caoutchouc-cells. They also closely 
resemble the caoutchouc-containing elements of certain Hippocra- 
teaceae 2 . In view of the fact that the caoutchouc-cells of Plagiopteron , 
together with those of Hippocrateaceae, &c., will form the subject of 
a paper ‘ On Caoutchouc-containing Plants ’ in a subsequent number 
of the Annals, I can limit my remarks here to a few general state- 
ments. 
These cells occur abundantly at the periphery of the pith around 
the groups of primary xylem and not so commonly in the secondary 
phloem. They are particularly abundant in the phloem of the petiole, 
in fact more so than in any other part of the plant. In the leaves 
they are chiefly found round about the vascular bundles, replacing 
part of the accompanying sclerenchyma ; but they also send slender 
branches into the mesophyll, which are best seen in surface view. 
The caoutchouc-cells are further abundant in all parts of the flower 3 
and fruit, but, since Plagiopteron has never formed seeds in any of 
the herbarium materials at my disposal, I was unable to determine 
whether they are also present in the embryo, which I however think 
very probable. Finally, it is worthy of note that the cells of the 
mesophyll contain large numbers of small irregular lumps of caout- 
1 Botanical Gazette, vol. xviii, 1893, p. 199; cf. also Solereder, Systemat. Anat. 
d. Dicotyl., pp. 176, 178. 
2 See Fritsch, Untersuchungen fiber das Vorkommen von Kautschuk bei den 
Hippocrateaceen. Bot. Centralbl. 1902, Beihefte, Band XI, Heft v, p. 292. 
3 I found them abundant in petals and sepals and in the walls of the ovary. 
Several run along to the tip of the style ; only a few are to be found in the filaments 
of the stamens, and these terminate at the point where the anthers commence. 
N 2 
