THE STEM OR SHOOT. 



143 



General Conclusions ox Adventitious Shoots. — As 

 regards the formation of adventitious shoots in general, 

 they seem to represent an attempt on the part of the 

 plant to reproduce itself more rapidly (/. e. by a short 

 cut) than by the normal method, whether this takes 

 the. form of vegetative or sexual reproduction. It 

 would also seem that very often adventitious shoots 

 arise as a result of the presence of some special 

 stimulus, such as excessive moisture or nutriment ; 

 in a mutilated organ the accumulation of nutriment 

 near the wound induces very accentuated tissue- 

 growth, the callus-cambium being stimulated to exceed 

 its function of mere callus-formation and to develop 

 a shoot. Where a great accession of nutriment occurs 

 owing to the activity of foreign internal organisms, as 

 in the Verbascum-le&t mentioned, unmutilated organs 

 may develop these buds just as freely. Quite as inter- 

 esting are those cases where the buds have become 

 fixed and stereotyped as a normal character of the 

 plant, and where no special or abnormal stimulus 

 appears to exist to induce their formation ; this has 

 simply been found to be a convenient method of re- 

 production, and being once assimilated into the ordi- 

 nary life-history, needs no extraordinary stimulus for 

 its production at the proper time and place. 



Some botanists have supposed that the production 

 of adventitious shoots by leaves amounts to a demon- 

 stration that there is no essential morphological dis- 

 tinction between leaf and shoot, and that in like 

 manner the root is homologous with the shoots which 

 it bears, etc. This appears to be a hasty and inade- 

 quate conclusion. The fact that a shoot arises adven- 

 titiously from a foliage -leaf, a root, or the integument 

 of an ovule, cannot surely reveal anything as to the 

 capacities and essential nature of the external form 

 of the organ bearing the shoot; the external form 

 and characteristics of the organ as a whole can hardly 

 enter into the question ; for in none of these cases are 

 there any genuine transitional stages between the 



