Ewart, The Relations of Chloroplastid aud Cytoplasma. 295 



darkness. If so, and if the cytoplasma only had been killed, 

 then here is a cage in which the „isolated" Chlorophyll grains 

 continue to assimilate. It must be remembered that it is by no 

 means so easy to be certain that the movement ceases in the 

 dark, as at lirst sight appears ; for, with normal chlorophyllous 

 cells showing active C02-assimilation, the evolution of Oxygen 

 and reeommencement of movement of the Bacteria is almost 

 synchronous M'ith the re-exposure to Jight, and may iollow it with 

 greater rapidity than the eye can be focussed on the preparation, 

 unless several trials are made. In all cases, however, if the 

 evolution of oxygen ceases in darkness and recommences in light, 

 the area of movement can be seen during the lirst few seconds 

 or first minute to spread out further and further from the source 

 of oxygen. But if the movement , thougli it appears only to 

 commence as the eye is focussed upon it, is seen to be from the 

 first quite active and to undergo no further perceptible increase, 

 then, it is quite certain, that its apparently instantaneous 

 reeommencement is an optical delusion, and that in the darkness 

 it has never really ceased to take place (p. 130. A^). 



It raust also be remembered that under certain circumstances 

 lateral diffusion along a filament may cause a faint evolution of 

 oxygen from a dead cell which is net to a living and activily 

 assimilating one. 



A dead wood fibre, mounted in or previously soaked in, meat 

 extract if lying parallel or near to, a green assimilating algal 

 filament, will appear to sliew, especially if very sensitive forms 

 are used but also though to a less extent with normal Bacterium 

 Tenno cultures, an evolution of oxygen which is dependent upon 

 light and ceases in the darkness. This is due to the Bacteria when 

 charged with oxygen being attracted by the nutriment to the wood 

 fibre which is permeated with it, and then after returning to the 

 source of oxygen supply, the Bacterium is again attracted by the 

 nutriment, and so on. In the absence of oxygen, i. e. in the 

 darkness, the movement and attraction cease. If Spirütum forms 

 are enclosed these are repelled from the source of oxygen but 

 not from the dead wood fibre. 



It is hence very essential that the Bacterium test should 

 always be applied in water, which may contain a trace of salts 

 but no nutriment. If sections of tissues are examined and these become 

 mucilaginous in water, a 2^/o sugar Solution may be used. From 

 the above, the extreme importance of being absolutely certain 

 that the Bacteria can obtain supplies of oxygen from no other 

 source but the one in which its evolution is being tested for, is 

 made clear. When relatively large portions of chlorophyllous 

 tissue are being tested, a correspondingly large number of Bacteria 

 must be enclosed. Any over-sensitivity of the Bacteria employed 

 may be a truitful source of erron. With over sensitive Bacteria 

 an attraction to, and apparent evolution of oxygen from, almost any 

 organic stiucture, may be detected unless proper precautions are 



