374 MR. S. LE M. MOORE's STUDIES 
of the grains are visible in both : the small mass upon the left 
shows very incomplete coalescence, if, indeed, mere cohesion be 
overstepped. Similar appearances were obtained from, among 
many others, wallflower mesophyll, after 22 days’ darkness, by 
which time coalescence was setting-in in cells of the palisade- 
tissue; Bryonia dioica (four days) Hydrocotyle vulgaris (a 
fortnight), Senecio vulgaris, Eschscholtzia californica, &c. In 
some of the palisade-cells of Hydrocharis Morsus-ranc the grains 
seemed to have coalesced after a week in the dark—at least it 
was found impossible to fully resolve the mass into its constituents. 
Such cases are, however, unsatisfactory, owing to the small 
size of the grains and the consequent difficulty in seeing them 
properly. l 
As in Vallisneria, the grains, when they come into close 
relation, become polygonal by mutual pressure*. Extreme iu- 
stances of this will be seen on reference to fig. 29b (Helianthus 
annuus) and fig. 31 (Bryonia dioica), each representing an arm 
of a mesophyll-cell in broadside view. In the first of these there 
are five grains, of which the central one has been greatly reduced 
in size aud rendered rectangular by the pressure of its four trape- 
zoidal neighbours. Lines of division are still to be made out, 
although it is possible that some amount of coalescence may have 
taken place. Fig. 31 shows the grains closely cohering, and 
perhaps in incipient coalescence, though this could hardly be 
the case if the well-defined white cross be, as I suspect, cell- 
protoplasm separating four grains t. 
Comparing figures of the chlorophyll body of Selaginella Mar- 
tensii (figs. 1 a, b,c) with those of coalescing chlorophyll grains 
(figs. 25 & 29), it is seen that in all there is a quantity of amor- 
phous chlorophyll contained in a limited space. Reason has been 
given for the supposition that if the upper-layer cells of a Sela- 
ginella leaf could stretch, fragmentation of the chlorophyll would 
ensue; and the same result we know happens when the pressure 
is relieved from coalescent chlorophyll by exposing it to epistro- 
phizing grades of illumination. Is there justification for going 
further than this, and holding that the massing (positive oF 
* On a subsequent occasion I hope to discuss this yielding to pressure in 
connection with the presumed dependence of the size and form of chlorophy u 
grains upon insolation. 
t I greatly regret not having solved the doubt upon this point; its import- 
' ance escaped me until it was too late in the year to repeat the experiment. 
