THE STEM OR SHOOT. 



127 



adventitious shoots definitely stereotyped as regards 

 their position on the leaf. As can be clearly seen in 

 some Coniferae, the leaf has both a decurrent and an 

 ascending foliar base ; where an axillary branch arises 

 it does so from the surface of the enlarged ascending 

 portion of the leaf -base. "Axillary" branching can 

 thus be best explained by assuming that in all, or most, 

 axes the leaves possess ascending foliar bases and that 

 lateral branches are produced upon these.* 



We will consider adventitious shoots according as they 

 arise on root, stem, leaf, and floral organs respectively. 



Eoot-Shoots. 



These are exceedingly common and widely spread. 

 Amongst the commonest are the well-known suckers 

 which arise from the roots of the plum, the elm, the 

 balsam-poplar, etc. (PI. IX, fig. 5) ; the willow (Salix) 

 and Sisymbrium Alliaria will also form them very 

 readily under certain circumstances. Gardeners pro- 

 pagate many plants by means of root-cuttings. Such 

 have been produced in Drosera hi/aris. The roots of 

 the bird's-nest orchid {Neottia Nidus-Avis) produce 

 root-buds almost as a normal character ; these usually 

 arise laterally ; occasionally, however, they arise at 

 the apex and congenitally replace the real root-apex. 

 This phenomenon has evidently misled some morpho- 

 logists, causing them to regard it as a case in which 

 the root develops directly, at the apex, into a shoot, 

 demonstrating thereby the essential identity in morpho- 

 logical nature of the two organs. This conclusion is 

 here regarded as erroneous : the above is merely a 

 case in which the adventitious lateral shoot has arisen 

 so close to the apex and so strongly that it has com- 

 pletely absorbed and replaced it ; for all that, it 

 remains the same adventitious shoot. A similar 



* On the phyton-theory, which is here held, the stem is really built up 

 entirely of leaf-bases ; hence axillary shoots can only arise on leaves in any 

 case. The development of the sporangium in Selaginella occurs in a way 

 which indicates the presence of an ascending foliar base ; and this will 

 entirely abolish the anomalous idea of its arising- on the stem. 



