MR. A. J. EWART ON ASSIMILATORY INHIBITION. 431 
oxygen is shown. After being kept in darkness for 3 days at 
‘30° C., the leaves are still green and normal in appearance, there 
is a marked diminution in the amount of starch present, and a 
fairly active evolution of oxygen is shown when exposed to light. 
That the more rapid stoppage of assimilation is due simply to 
the more rapid accumulation of carbohydrates, and not to any 
poisonous depressant influence of the CO,, is shown by the fact 
tbat leaves of Vitis vinifera and V. Labrusca kept in an atmo- 
sphere containing 10 per cent. of CO,, but exposed to very weak 
-diffuse daylight, show after 4 days no perceptible accumulation of 
starch and an active evolution of oxygen on examination. 
In experimenting with Mosses, it is practically impossible, if 
the entire plants are used and kept in ordinary air, by even full 
and prolonged exposure to light to cause a maximal accumulation 
of carbohydrates and consequent stoppage of assimilation, for 
the starch and sugar are being continually transferred to the 
growing parts and used there for the formation of proteid and 
cellulose. If, however, the young growing apices are removed and 
plants kept stuck through thin slips of cork floating on water, 
isolated from one another, fully exposed to light, and in an 
atmosphere containing from 10 per cent. to 15 per cent. of CO,, 
quite definite results are obtained. Thus after 5-6 days expo- 
sure the leaves all remain living, but show no evolution of 
oxygen (Dicranum scoparium, Catharinea undulata, Bryum 
ceespititium, Mnium stellare). In Catharinea the cells are quite 
granular, with starch grains both enclosed in the chlorophyll 
„grains and lying free in the protoplasm. In Bryum the chloro- 
phyll grains are swollen with one or more centrally placed starch 
grains, and abut on one another so as to be polyhedral instead of 
‘spherical as normally. In Mnium the protoplasm is finely 
granular, but the granules do not stain with iodine. Starch is 
present only in the chlorophyll corpuscle and in the form of a 
‘single large central grain. In Dicranum the protoplasm is 
granular, opaque, and contains an abundance of oil, whilst each 
chlorophyll grain contains a rather small but distinct starch 
grain, commonly absent from normal plants. Here starch 
appears only to be formed when an excess of oil and sugar are 
present. After the plants have been kept for 1 day in darkness 
at 30° O. in a damp well-aerated atmosphere, a weak power of 
assimilation is shown by most leaves of Mnium and Bryum, at 
the bases of the leaves in Catharinea, and in the younger leaves 
