THE HIGHER CRYPTOGAMIA. 285 



longer spreads out under pressure. Sulphuric acid dissolves 

 the outer layer the inner one withstands its action but 

 assumes a brown colour. At this period of development 

 the diameter of the cell is from 20*24 to 23 60 m. m. m. 

 and no trace of any third inner membrane is perceptible, 

 even when the cell is ruptured after lying in alcohol. 



But when the cell has attained a diameter of from 303 

 to 37 m. m. m. a third internal covering of the cell-content s 

 soon makes its appearance. Such a cell when placed in 

 diluted alcohol exhibits three perfectly distinct membranes. 

 Each of the three globular vesicles is situated excentricallv 

 in the interior of the next outer one. If the fresh cell is 

 placed in alcohol the three membranes swell up but in dif- 

 ferent degrees : the outer one swells the most, the middle 

 one to a less extent than the outer, and the inner one least 

 of all. The cell-contents swell up at the same time ; they 

 always remain closely attached to the inner membrane, and 

 cannot be brought to contract into a smaller space than 

 the cavity of the latter. In a cell for instance whose diameter 

 in alcohol was 30*2 m. m. m. the membrane immediately 

 enclosing the cell contents measured (after treatment with 

 water) 32 m. m. m.; the middle one 37'04 m. m. m. ; and 

 the outer one 63*84 m. m. m. 



At this stage of development the iodized solution of 

 chloride of zinc colours all three membranes blue ; t he- 

 middle one changes colour first, and its colour is the most 

 intense. If such cells, after lying in alcohol, are ruptured 

 by pressure, the membranes, which have previously been 

 closely attached to one another, separate ; the middle one 

 contracts to a smaller space than the outer one, and the 

 inner one more than the middle one. After contrac 

 tion they still retain the form of tense globular vesicles, 

 and exhibit a Greater thickness of wall than before. If 

 cells fresh from the sporangium are treated with water, the 

 outer and middle membranes often swell up to some extent : 

 they separate from the inner layer, remaining at the same 

 in close connexion with one another. The distended mem- 

 branes are easily separable from one another by pressure, 

 and they exhibit a scarcely perceptible increase in thickness. 

 At this period no trace is yet visible of the course of the 



