BOTANICAL SUBJECTS. 159 



In the rhizomes of seaweeds and ferns there does not appear 

 to be any such thing as an axillary bud. It is the terminal bud 

 which is axillary-like to the tipmost frond. This terminal bud by 

 further lengthening leaves the tipmost frond behind without an 

 axillary bud. In the section on axilliary buds I have endeavoured 

 to put in words the conception of the genesis of the axillary bud 

 of ph^enogams. 



In the potato tuber a group of nodes become independent by 

 the decay of the internode which supported them. The same 

 happens in Vitis Pterophora^ according to Greorge Nicholson. 

 The group of nodes at the end of its branch grows into a tuber, 

 which falls off and forms a new plant . 



The rhizome being a prolongation of the cellular basis of the 

 frond has acquired the habit of producing roots opposite the 

 frond. This habit we see is still inherited in many plants, whose 

 stems no longer creep along the ground, but are erect. There are 

 innumerable examples of plants which give off aerial roots from 

 the nodes of their stems, as a habit inherited from the rhizome 

 stage. Ferns, grasses, arads, orchids, and many others have this 

 habit. These aerial roots now mostly serve the purpose of attach- 

 ment and fixation or support of the weak, erect stem, which 

 originally was a creeping stem with roots in the ground. Pepper- 

 mint has both creeping and erect stems, the latter being only 

 branches of the former. The potato, the vetch, and others have 

 the same. In some, roots are still developed from the nodes ; in 

 others, this habit is temporarily lost, though under certain cir- 

 cumstances it is easily revived. In the case of the mint, the 

 suj)pression of roots on the upright branches may be partly due to 

 the energy being taken up wholly by the leaves, and partly to 

 atrophy by disuse. 



Cuttings of plants placed under favourable conditions form a 

 callus at the cut end, from which roots are emitted. This callus 

 may correspond to the cellular corm-like body, called the disk, by 

 which rootless seaweeds are attached to rocks. It appears to be 

 the mother tissue of roots. 



The corm of the Cyclamen would also correspond to the 

 seaweed disk of attachment. According to this view, we would 

 have the stem equal to a rhizome, the rhizome to a corm, and the 

 latter equal to the minute stump of cellular tissue at the foot of the 

 seaweed frond. 



