836 
MR, W. GARDINER ON THE CONTINUITY OF THE 
much greater.* When stained with chromic acid the protoplasm of the tannin cells 
exhibits a distinct appearance of reticulation, but from what cause I am at present 
ignorant. 
Amicia zygomeris .—The pulvinus of this highly interesting plant was pointed out 
to me by Professor Sachs as well worthy of investigation. As a most striking 
example of both periodic and irritable movements this plant has apparently escaped 
general observation. It is particularly sensitive to alternations of day and night, and 
assumes the sleep position long before even such plants as Robinia. If violently 
shaken the leaves will, after a time, fall, and will be similarly affected some time after 
being cut and placed in water: the large size of the leaves rendering the least 
movement very conspicuous. Since it was the secondary pulvini that were especially 
movable, and they were, at the same time, of a comparatively large size, I used them 
in preference to still larger main pulvinus. 
The chief characteristics of the pulvinus tissue of Amicia are the thinness of the 
walls of the parenchymatous cells, the extremely unlignified character of the vascular 
bundle and the remarkable development of a system of large pits, which is in 
this case extremely pronounced. The whole tissue is very succulent, and easily 
admits of thin sections being cut (Plate 68, fig. 9). 
On treating with iodine and Chlor. Zinc Iod. the pits are, as usual, markedly 
brought into view. From the contrast of the deep blue coloration of the walls with 
that of the pits, it appears, at first sight, that no staining of the latter has taken 
place. Sections transverse to the pit, however, show that both a very slight staining 
of the pit-membrane has occurred, and that the membrane is extremely thin. In 
some of the pits small masses of protoplasm may be recognised sticking to the pit- 
membrane, being brought into view in consequence of their brown staining reaction. 
The pit-membrane is well stained by methylene blue. Scarcely any difference can be 
detected between the thickness of the cell-walls on the upper and under sides of the 
pulvinus. Except just beneath the epidermis, and next the vascular bundle, the cells 
are relatively large. The layer of protoplasm (primordial utricle) lining the cell-wall 
is thin, and the central vacuole is large. In consequence of this, very great shrinking 
of the protoplasm is possible, and experience shows that the successful preservation of 
this tissue is extremely difficult. Any reagents causing the least diffusion very soon 
affect the protoplasm, and the only at all successful treatment is brought about by 
* The fact deserves notice that in the cases where the protoplasm displays any great activity of 
function, the cells of such a tissue usually contain tannin. For example, pulvini of Mimosa Robinia, 
Desmodium, &c., leaf of Bioncea, Drosera. Again in galls, where a stimulation of the protoplasm 
followed by rapid growth occurs. Notice that in Robinia it is the pulvini of the leaflets that move more 
than the main pulvinus, which have the greater quantity of tannin. The effect of tannin in producing 
aggregation is dealt with by A. E. W. Schimper (‘ Rot. Zeit.,’ 14, 1882) On Tannin. See also 
Gardiner “On the General Occurrence of Tannin in the Vegetable Cell, and a Possible View of its 
Physiological Significance,” Proc. Camb. Phil. Soc., vol. iv., pt. vi., pp. 387-394, and Bot. Central. 
Bd. xvi., No. 48, p. 258. 
