THE STEM OR SHOOT. 



117 



plant is reduced to a basal rosette from the axils of 

 whose leaves the sessile flower-heads arise. 



Grates observed among his cultures a plant of 

 Oenothera Lamarckiana X graitdiflora, whose stem, 

 although forming a considerable number of leaves, 

 remained as a rosette, without elongation of its inter- 

 nodes, for fifteen months, after which it elongated and 

 bore flowers. 



Again, Klebs, by placing the plant under special 

 conditions, induced both the runner and the flowering- 

 stem of A jug a rejpians to become changed into rosettes 

 of foliage-leaves. 



Asparagus possesses underground, thickened rhi- 

 zomes and aerial elongated stems. Grevillius mentions 

 a very rare case in which many of the basal branches 

 of the aerial stems in A. Sprengeri became, for some 

 distance above the level pf the ground, transformed 

 into quite short, thick, tuber-like rhizomes. 



Internode suppression occurs normally in all rosette- 

 forming plants. 



2. Op Axillary Shoots. — The converse condition to 

 that of abnormal axillary branching is that of the 

 complete or partial suppression of lateral axillary 

 branches. In the spruce {Picea, excelsa) and silver-fir 

 {Abies pectinata) individual trees have been found in 

 which the formation of lateral branches was entirely 

 suppressed ; another variety, termed by Caspary 

 virgata. and by Carriere denudata, possesses lateral 

 branches of the first order only which extend hori- 

 zontally from the main stem and give the tree some- 

 what the habit of an Araucaria imbricata. The branch- 

 less condition in the above cases is pretty obviously due 

 to the unfavourable situation of the trees concerned, 

 as in the midst of a dense plantation, where the neces- 

 sary supply of light and air, and therefore of nutrition, 

 would be wanting. Yet, in order to account for the 

 fact that single individuals only are affected in this 

 way, a part of the cause must doubtless be ascribed to 

 some peculiarity in the constitution of the plant. 



