MONOCOTYLEDONEJE. 37 



and pierced at pretty regular distances by some of 

 the horizontally lying cells, Fig. 9, forming stomata 

 or openings for the emission or admission of aerial 

 fluids. The exterior is also in some cases remarkably 

 smooth and glossy, and ultimately becomes membra- 

 nous, i. e. dense cellular matter and of considerable 

 tenacity. 



It is from the compound character of the corculum 

 or crown of these plants, that, under favourable cir- 

 cumstances of soil and season, the annual species are 

 so productive of thick and heavy crops. On very 

 inferior land a seed may only bring a single culm and 

 ear to perfection, whilst on rich land from seven 

 to twenty is the usual produce. From the same 

 circumstance it is, that the perennial species spread 

 themselves on the surface and form so thick a turf. 

 In both cases this property may be excited by the 

 operation of the sithe or close-grazing animals 

 preventing the seeding of the plants. Such mutila- 

 tion, frequently repeated, even changes the nature 

 of some species so much, that annuals become 

 biennials, and biennials almost perennial in duration ; 

 and this merely from denying them the principal aim 

 of their being, the production of seed. 



There is another kind of mutilation which in- 

 creases the volume and produce of grasses ; it has 

 been already observed, that each culm has its own 

 system of roots, but which remain inert if the culm 

 itself be not called into action ; when, however, the 

 primary productions are cut, eaten over, or trampled 



