ZOOLOGY AND BOTANY, MICEOSCOPV, ETC. 63 



treatment with alcohol, yields an intermediate product known s,s proto- 

 chlorophjll ; thus leucophyll is transformed into chlorophyll in living 

 tissues under the influence of light, but into protochlorophyll in deact 

 tissues under the influence of alcohol and other chemical reagents. 

 When the tissues are killed by drying or freezing, a mixture of proto- 

 chlorophyll and chlorophyll is formed. The amount of protochlorophyll 

 varies slightly in proportion to the amount of starch and light. These 

 results are partially explained if it is assumed that the transformation 

 of leucophyll into protochlorophyll takes place owing to the influence of 

 some substance in the cell-sap ; when the plant is frozen or dried the 

 protoplasm is killed but the leucophyll is more or less protected from 

 the action of this substance. Water or damp air favours the formation 

 of protochlorophyll. The authors discuss the question as to whether 

 leucophyll is colourless or a special pigment in a second paper.* The 

 experiments dealt with the spectra of chlorophyll and allied substances 

 fo-ind in living and dead green and etiolated plants, and were con- 

 ducted by means of a new form of apparatus devised by the authors. 

 It appears that the living plastids of green plants are able to form two 

 different green pigments, i.e. chlorophyll and protochlorophyll, both of 

 which are fairly stable, but more particularly the latter. Both pigments 

 are derived from a pigment known as chlorophyllogen, a very unstable 

 compound, which is converted into chlorophyll under the influence of 

 light or into protochlorophyll under the influence of certain reagents. 

 Protochlorophyll is not changed into chlorophyll by light. A few plants 

 are able to form chlorophyll from chlorophyllogen in the absence of 

 light, owing to the presence of some unknown chemical reagent con- 

 tained in the cell-sap. Protochlorophyll and chlorophyll are closely 

 related, as seen by the similarity of their spectra and their behaviour 

 towards acids and alkalis, but protochlorophyll breaks down into proto- 

 chlorophyllan most quickly under the blue rays, and chlorophyll into 

 chlorophyllan most quickly under the red rays. Protochlorophyll is 

 unaffected by light in the presence of alkalis, but quickly decomposed in 

 the presence of acids. Chlorophyll never arises directly from a colour- 

 less chromogen, but under the inflaence of light and of cert lin reagents, 

 from a coloured pigment, itself derived from an unknown colourless 

 chromogen previously formed. Thus chlorophyll-formation is not a 

 simple photochemical process, as claimed by some authors, although 

 light is an important factor. 



Irritability. 



Action of Light on Chlamydomonas.f — P. Desroche describes the 

 action of divers rays of hght on the movement of zoospores in Chlam//- 

 domonas. Four bands of the spectrum are absorbed by the chlorophyll 

 of this alga, namely. A, h, ¥, P>, and these are separable into two groups. 

 On the one hand the band A excites the movement of the zoospores. 

 On the other hand the bands b, b^, B tend to hinder the movement, B 

 much more energetically than the other two. 



* Biol. Centralbl., xxxi. (1911) pp. 481-98 (1 fig.), 

 t Comptes Rendus, cliii. (1911) pp. 829-32 (figs.). 



