MICROSCOPIC OBJECTS. 12 



Fig. 23. Siliceous Cuticle of Sugar-grass (Holcus 

 saccharatus) , x 120. 



Siliceous cuticles are found chiefly in the Glumacese and 

 Equisetacese. The cells of this cuticle are rather large, and 

 the stomata small the latter having two guard-cells instead 

 of four, as in figs. 22 and 24. 



The cuticle of this grass is easily prepared, the deposit of 

 silex being rather abundant. The best plan is to soak the 

 grass in water for about 24 hours, and then to boil in nitric 

 acid |, water |, for a short time, when the siliceous cuticle 

 will separate ; or it may be boiled in the pure acid. It may 

 then be mounted in liquid, or dried and mounted in balsam 

 for the polariscope ; but glycerine is best. 



Fig. 24. Cuticle of Araucaria (Araucaria imbricata), x 120. 



This cuticle of the Chilian Pine, on testing with the acids, 

 burning, &c., I find is not siliceous as is generally supposed, 

 but appears to consist of a tough cuticle highly imbued with 

 a resinous substance, so as to be inflammable at a burning 

 temperature. The stomata seem to have four " guard-cells," 

 two lower and two upper. In some leathery cuticles, the 

 cells surrounding the guard- cells appear to be elevated above 

 the surrounding surface. 



This object may be prepared by boiling the leaf in nitric 

 acid, and mounting the cuticle so separated in any good 

 liquid. Or it may be dried and mounted in balsam as usual. 



