278 Mr Philip Sewell on the [sess. lit. 



piiscle, obtained by it by the reduction of proteids in the 

 cell, disappears as the etiolin is formed, being in part used in 

 building up the protoplasm of the corpuscle, which proto- 

 plasm in turn goes to the production of the colour-substance. 



As to stages subsequent to the production of the chloro- 

 phyll, Schimper and Baccarini have recorded that, from the 

 round chloroplast may be formed a body of crystalline 

 character, and of red or yellow colour, invested by a layer of 

 protoplasm. 



Evident conditions- of degradation are commonly seen in 

 fading leaves, where the chlorophyll-corpuscles either undergo 

 disintegration, the whole leaf becoming brown, or collect 

 together into amorphous masses ; these, although at times 

 difi'erently coloured, are most commonly rendered yellow by 

 the presence of xanthophyll. This xanthophyll is the sub- 

 stance into which the chlorophyll has chiefly altered. 



Messrs Martin and Thomas have recorded several inter- 

 esting observations as to the condition of the cells in leaves 

 which, as in autumn, are undergoing colour-change. When 

 red, the denser cell-contents have mainly disappeared, the 

 colour being free in the cell-sap ; when yellow, the colour is 

 chiefly in the amorphous masses, the change evidently not 

 having proceeded so far. The subsequent brown stage is one 

 of complete decomposition, without any signs of vitality such 

 as are exhibited with the other colours. 



Colours occur most commonly as follows : — 



White. — Either as plastids of an almost transparent or a 

 very pale yellow colour, when the whiteness is not of a pure 

 kind. Whiteness, however, is generally due to the presence 

 of air in the tissue of which the part consists, and this allows 

 of nearly total reflection ; the cause being exactly similar to 

 the cause of the whiteness of snow. Kose-coloured geraniums 

 example the combination of cells containing air witli others 

 underneath containing red colouring matter. 



YMow is fixed as etiolin, in leaves or in certain flowers (it 

 has an evident similarity witli Krukenberg's " lippochromes") ; 

 or as fhiid xanthojiliyll in leaves or many (? most) flowers. 



Red ai)p(!ars at times attached to ordinary chromoplasts, 

 at times in the form of crystals or globules, either with or 

 without an investing layer of protoplasm ; more generally it 

 occurs in the cell-sap produced immediately, or mediately 



