BOTANICAL SUBJECTS. 157 



What are called internodes in the rhizome or stem are the 

 least important parts of a plant. The nodes are the centres of 

 action. They are repetitions of the elements of the stem, and 

 held together by the internodes. 



One can imagine in j)rimordial times a swampy piece of land 

 swarming with rhizomes of different kinds struggling with each 

 other for mastery, like tentacles thrown out in all directions, by 

 a crowd of polyps. One can easily see that the rhizome, which 

 could bend itself upwards, grow into the air, and become a stem, 

 would have immense advantage of light and air. The aerial stem 

 would help its rhizomes, and these, the stem, and the whole colony 

 would flourish, not of course without modifying itself to suit the 

 change of medium. 



The principal function of internodes is to separate the nodes, 

 according to needs, for the purjDose of better aeration and illu- 

 mination in a crowded space, while at the same time they keep 

 the colony together for mutual support. 



In some cases, however, the internode decays, leaving the node, 

 or group of nodes, isolated as a tuber, or tubercle, with a store of 

 food for commencing an independent life. This excision of nodes 

 by decay of internodes will be seen to be of great importance. It 

 preserves to the species any useful qualities already acquired, while, 

 at the same time, it disseminates growing points or buds, and thus 

 exposes them to new conditions, where the nutritive elements have 

 not been already exhausted by that plant. 



This process is imitated by the horticulturist, when he chops 

 up a vine-stem into nodes. These, however, will always produce 

 the same variety. 



The foregoing conception of the genesis of a rhizome is such 

 as might come about by the arrested fission of a monad. 



Now, let us suppose a seaweed already developed into a form 

 like that of Jania fastigiata (Fig. 48), with only a small disk of 

 attachment, all the rest being filiform fronds, dividing dichoto- 

 mously, or developed only a step further, into the form of Callitham- 

 7iion Griffithsioidts (Fig." 49), ^vith the disk of attachment splitting 

 up into fibrils ; is it possible for a rhizome to have its genesis in 

 su ch root-disks as these ? 



It will be evident, on a little consideration, that the separation 

 of the bunch of fronds, when these have become too crowded, 

 would result in one of two things. Either the disk would split up 



