UTRICULAR STRUCTURES. 183 



cles also undergoes an alteration occasionally, consisting 

 in the colour becoming fainter; moreover, even in the 

 transition of one colour into another. In many genera 

 of FlorideaB it is rather common for the red colour-utri- 

 cles to become subsequently green or yellowish green. 



The colour-utricles undergo dissolution in three ways : 

 1, by propagation ; 2, by the starch-globules inclosed 

 within them gradually displacing the colouring matter, 

 and at length causing the absorption of the membrane ; 

 and, 3, by changes in the cell-contents, inducing a solu- 

 tion of the contents and membrane. 



When the solution of the colour-utricles is brought about 

 by changes in the cell-contents, they usually become de- 

 tached from the cell-wall, pass into the interior of the cavity 

 of the cell, and acquire a more or less perfectly globular 

 form. The colouring matter becomes granular, loses its 

 colour, and is then dissolved, the membrane at the same 

 time disappearing. In decaying cells of the pro-embryo 

 of the Ferns, as well as occasionally in decaying cells of 

 the leaves of the Hepaticse and Mosses, I have seen the 

 chlorophyll-utricles expand considerably during this pro- 

 cess (in Pteris nemoralis from "006 to *008 of a line). 

 The chlorophyll dissolved into minute dark granules which 

 swam in a colourless fluid. The membrane of the utricle 

 was here very distinct. (Fig. 10, d, e,f.) 



7. Starch-utricles, Starch-granules. 



Three different opinions have been expressed as to the 

 origin and nature of the starch-granules. According to 

 one, they consist of a cell-like envelope and fluid con- 

 tents. According to a second, a nucleus is first formed, 

 around which concentric layers are deposited on the out- 

 side. According to a third view, the formation of the 

 layers proceeds from without inwards. 



The first opinion, Raspail's, appears in a peculiar form, 

 resulting from his theory of cells. The starch-grain is a 



