290 Ewart, The Relation of Chloroplastid and Cytoplasma. 



without having seeu the original paper giving an account of thein 

 is rather a Iiazardous proceeding. 



On the question as to whether the isolated Chlorophyll body 

 is capable of independent CO 2 — assimilation Kny and Kolk- 

 witz obtain contradictory results to Engelmann, Haber- 

 ia ndt and myself. The explauation of their failure to obtain posi- 

 tive results is seen at once on referring to the text. In the first 

 place the authors worked in nearly all cases with impure cul- 

 tures, made, without adopting any precautions whatever, by allo- 

 wing meat to decompose in water. The resulting Bacterium con- 

 taining putrescent and poisonous fluid was markedly alkaline, 

 but was, nevertheless, added directly to the isolated Chlorophyll 

 giains. It has however been shown (p. 415 A^) that even weak 

 alkaline Solutions exercise a marked injurious effect upon the 

 Chlorophyll grain, even when in the intact cell, depressing or 

 inhibiting its assimilatory powers. Naturally the isolated Chloro- 

 phyll body will be very much more sensitive. 



To obtain isolated Chlorophyll grains Kny and Kolkwitz 

 adopted a different method to that employed by Haberia ndt 

 and myself. Their method does not seem, to judge by their nega- 

 tive results, as capable of yielding uninjured Chlorophyll grains, 

 as the simpler method, in which everything depends upon the 

 manipulative skill of the Operator. 



A third and most fatal objection lies in the Statement by the 

 authors, that they found ringing the coverslip with vaseline to be, in 

 the absence of air bubbles and assimilating organisms, unnecessary ! 

 As has been already shown, the most careful ringing to exclude 

 all external oxygen is an absolute necessity for accurate experi- 

 mentation. Thus in thinly ringed cell preparations, even if a few 

 Bacteria are enclosed, sufficient oxygen may diffuse in to keep 

 an end cell of Ohara alive and shewing slow rotation for a 

 period of days extending to more tlian a week in some cases, 

 though kept in contiuuous darkness. (p. 420 A^). 



I have repeated some of my previous observations, using un- 

 ringed cell preparations but have found it quite impossible under 

 such conditions to obtain any reliable results. The reason for 

 this is twofold. Firstly, the most actively reacting Bacteria, collect 

 at the edges of the coverslip where there is an abundance of 

 oxygen and leave the centre of the field where there is but very 

 little oxygen; and secondly, owing to the evolutiou of oxygen 

 from the isolated chloroplastid beiug always weaker, and generallj 

 much weaker, than from an algal cell of the same size or from 

 the same normal grain, the amount of oxygen which it evolves is 

 insufficient owing to the relative abundance and hence compara- 

 tively high partial pressure of the surrounding dissolved oxygen 

 which has diffused in at the open edge of the coverslip, to 

 markedly attract the surrounding bacteria in the centre of the 

 preparation, which, it is worthy of notice, are, as has been seen 

 above, the less actively re-acting ones. 



