Ewart, Can Isolated Chloroplastids Continue to Assirailate? 
35 
no movement of the bacteria was produced, then it was con- 
cluded that no power of assimilation was present. In every 
case, the optimal illumination was taken as the point beyond 
which no further increase in the evolution of oxygen became 
perceptible. 
As regards the evolntion of oxygen from isolated Chloro¬ 
phyll bodies, that algal cells were not mistaken for these is 
quite certain, for in all the cases given, certain of the chloro¬ 
plastids were watched nntil they died, when the usual alterations 
of form and contour could be seen to take place. Moreover, in 
all cases the chloroplastids which occasionally continue to exhibit 
an evolution of oxygen in the light when isolated, ceased to 
assimilate and died in from 2 to 6, or occasionally 8 to 10 
hours; whereas algal cells enclosed in a similar preparation 
remain living for an indefinite length of time. The application of 
plasmolytic tests was therefore not considered necessary, and 
would moreover have been extremely difficult. The fact that 
only few of the isolated chloroplastids ever shew any evolution of 
oxygen and these only from certain plants, and that it is always 
weak in character, is not at all surprising, but only to be expected 
considering how drastic the most careful mode of preparation 
necessarily is. 
Kny’s objection that an investing film of cytoplasm might 
have remained attached to the chloroplastid is a much more 
pregnant one. He has indeed seen an evolution of oxygen take 
place in certain cases from Chlorophyll bodies to which a little 
cytoplasm adhered. In my own experiments, the occasional 
Chlorophyll bodies in which a weak power of assimilation could 
still be detected were not tested until they had died, and then 
only by means of lodine, even that being a matter of some 
difficulty and possible only because the chloroplastids are frequently 
found to adhere slightly after several hours to the slide or 
coverslip*). Tested by such means and examined when living 
under high powers, chloroplastids, apparently free from all 
external cytoplasm, were found still to be able to assimilate 
carbonic acid. 
In any case the distinction is not so important a one as it at first 
siglit appears to be. The chloroplastid is a plasmatic organ, built up 
of a specially constituted cytoplasmic framework and thus forming 
an assimilatory mechanism, of which the Chlorophyll is simply an 
accessory part. Moreover on theoretical grounds, the existence 
of a plasmatic film (Pfeffer’s „Plasmahaut“) of almost mole- 
cular tenuity around the chloroplastids may be concluded with 
comparative certainty. This membrane would be in visible under 
the highest powers whatever stains were used, and yet if such 
a diosmotic membrane clothes the chloroplast, it will be only 
when this is maintained intact that the latter can continue to 
*) Assim. Inhib. Jour. Linn. Soc. Bot. Vol. XXXI. p. 4 ; 26. 
3* 
