Form of Horniidium fictccidum , A. Braun . 527 
of the granule assuming a deep blue colour, while the thin external layer 
becomes merely light blue. The fact that the outer portion of the granules 
behaves rather differently from the interior towards reagents indicates that 
the structure of the granules is possibly vesicular, the contained substance 
differing somewhat from the bounding layer. Such a structure would be 
-comparable to that recorded for the granules of Zygnemaceae (cf. p. 523). 
Commenting on the special abundance of granules in a heath form of 
Zygnema ericetorum , and their formation into a dense peripheral layer in 
time of drought, Fritsch 1 observes that one might be disposed to associate 
the granular layer with the great power of resistance to drought possessed 
by this Alga. The question appeared of some importance in connexion with 
Hormidium flaccidum , which, though capable of considerable resistance to 
desiccation, shows none of the usual xerophytic adaptations, e. g. thick 
mucilaginous walls. Since granules are not habitually present in the cells, 
general observations were made to trace some relationship between 
desiccation and the appearance of granules, and also to reveal the power of 
resistance to drought possessed by granular material. 
As a result, it was found that during periods of desiccation, both in 
summer and winter, granules always occurred in a large proportion of the 
living cells, but were frequently minute and scanty. When the Alga was 
receiving continuous supplies of water, the granules were sometimes 
prevalent in the cells, at other times localized in a small proportion of them. 
The latter variation apparently depended on the temperature and amount 
of sunshine. During winter, when the soil was continuously damp, the 
granules were often entirely absent, and, when present, were usually small 
and restricted to a minor proportion of the cells (25 per cent, and 46 per 
cent, in different samples collected in mid-winter). During warm, sunny 
weather, 2 they appeared in most of the cells, and were both large and 
abundant. These observations indicated that granules do arise as a result 
of desiccation, though at such times they may be small and scanty ; but 
they also appear, often in abundance, under other circumstances, viz. warm, 
damp sunny weather. 
To observe more accurately the resistance of the cells to drought and 
the effect of the latter in producing granules, experiments were set up to 
subject the Alga to continuous drought, the other conditions of growth 
being so far as possible untouched. A large patch of Hormidium , with 
a considerable thickness of underlying soil, was collected from the native 
habitat and examined at frequent intervals during the experiment. 
In Experiment I, which lasted from the end of January to the middle 
of March, the piece of soil was laid on a glass Petri dish and kept out of 
1 l.c., p. 145. 
2 Observations were made on material transplanted, with considerable depth of underlying soil, 
to a greenhouse. 
