THE OXIDASES IN RELATION TO PIGMENTATION 287 



of this process in a number of tissues, such as the epidermis 

 of the floral leaves of Iris germanica, in the leaves of the 

 rose, of the walnut, in the seedling of Ricinus, and in the 

 tuber of the potato. No description can be as illuminating 

 as a glance at Guilliermond's (1914, 1) coloured plates. In 

 the rose leaf, however, the sequence is much as follows : 

 In very young cells mitochondries of elongated form are 

 visible, and are grouped irregularly round the nucleus. In 

 slightly older cells these filaments have become more 

 highly refractive, and are considered to contain a phenolic 

 substance, which is colourless in the rose, but is sometimes 

 of a faint yellow shade in other plants. 



Cells which are still further developed contain a pale 

 pink anthocyanin in the mitochondries, and in the next 

 stage the colour is intensified, the filaments are thicker, 

 and their ends have become club-shaped. This enlarge- 

 ment of the extremities continues, until a constriction in 

 the middle severs the connection, as is usual when a drop 

 of liquid possesses a length which exceeds the limit of 

 stability for the ratio of length to diameter. The droplets 

 formed in this manner then coalesce, so that the cell is 

 largely occupied by one or more deep red vacuoles. The 

 rapid increase in volume of the latter results in the dilu- 

 tion of the anthocyanin, so that individually they are of a 

 lighter shade, though the macroscopic appearance is un- 

 altered, as the total amount of pigment has not varied. 



There is some evidence that the mitochondries themselves 

 possess a lipoid membrane supported by an albuminoid 

 framework. Various hypotheses have been put forward as 

 to their mode of action. Regaud (1911), for example, con- 

 siders that they have a selective action upon certain sub- 

 stances elaborated by the protoplasm. This is, after all, 

 only another way of stating the fact that these substances, 

 are observed to accumulate within the chondriome. 



