604 Church . — The Structure of the Thallus of 
explanation : in direct relation to the energy of the assimi- 
latory processes going on in the chlorophyll-corpuscles, 
a precipitation of calcium carbonate is formed in the sur- 
rounding medium ; that part of it which deposits in the 
mucilaginous sheath will be ‘ fixed/ the rest will be washed 
away ; further deposition takes place uniformly throughout the 
mucilaginous layer, and calcification becomes more and more 
intensified in direct proportion to the activity of the chloro- 
phyll-corpuscles in the immediate vicinity. A suggestion that 
the maximum precipitation is not utilized in N eomeris dumetosa 
owing to scanty development of the mucilaginous layers, is 
afforded by the observation that calcification extends down 
the pedicels of the aplanosporangia to about a distance equal 
to nearly twice the thickness of the deposit over the spherical 
portion (Fig. 30, 31) ; and this, again, agrees with the pheno- 
mena described by Cramer 1 for Cympolia , the young parts of 
which are endowed with a copious mucilage. That the apex 
and upper twenty whorls or so show scarcely any trace of 
deposit in their mucilaginous sheaths may be due to the rate 
of growth being greater than the rate of deposition ; but, 
more probably, it is to be explained by the assimilatory 
processes being less energetic in the growing whorls than the 
respiratory, so that, even were a deposit formed, the parts 
would tend to decalcify owing to excess of carbonic acid in the 
neighbourhood. It is not so easy, however, to suggest why 
calcification should not set in until Stage IV is well advanced. 
Precipitation will vary with the amount of calcium in the 
water, the intensity of the light, and the assimilatory activity of 
the chlorophyll-corpuscles in the segments ; but, as the plants 
are colonial, and the clumps contain specimens in all stages of 
growth, the first two factors will be fairly constant, and it can 
only be concluded that it is at this stage that the intensity of 
chlorophyll-assimilation first becomes sufficient to destroy the 
equilibrium of the solution of calcium bicarbonate. It is 
interesting to compare De Bary and Strasburger’s observations 
1 Loc. cit., p. 19. 
