10 STRUCTURE. 



great nuisances. A few species have bulbous roots, the 

 base of the stem becoming spherical and sometimes pro- 

 ducing other bulbs from its side. 



The stem is generally cylindrical and hollow in matu- 

 rity. Lindley explains it to " exist in two different states, 

 that of the rhizome and of the straw, — the rhizome, 

 which is the true trunk, and the straw, which may be 

 considered a ramification." He says, "The rhizome 

 grows slowly, and differs in no respect from the stem of 

 other monocotyledonous plants, as is evident in that of 

 the bamboo. The straw, on the contrary, which grows 

 with great rapidity, is fistular, with a compact impervious 

 diaphragm (the node) at each articulation. In the be- 

 ginning, when this straw was first developed, it was a 

 solid body like the rhizome, only infinitely smaller ; but in 

 consequence of the great rapidity of its development, the 

 cellular tissue forms more slowly than the woody vas- 

 cular bundles which it connects, and, in consequence, a 

 separation takes place between the latter and the former, 

 except at the articulations, where, by the action of the 

 leaves and their axillary buds, is formed a plexus of 

 vessels, which growing as rapidly as the straw, distends, 

 therefore never separates in the centre." The stem of a 

 grass is hollow as a rule, but there are one or two ex- 

 ceptions, as the Sugar-cane. Generally, the stem is 

 cylindrical, but it is sometimes compressed, as in the case 

 of Poa compressa. It has a siliceous coating, more or 

 less developed, and flint is formed in the joints. 



Lindley 's description of the stem justifies our calling 

 the lower part, occasionally procumbent and rooting, the 

 rhizome, the naked ascending part the stem proper, and 

 the upper part, to which the spikelets are attached, the 

 rachis. The stem is simple, any branches that occur 



