VEGETATIVE PROPAGATION 



247 



Fig. 170. 



Leaf of Bryophyllum after culture on moist soil, with 

 adventitious buds borne at its margins. 



not normally present, serve the same end, but they are less frequent. 

 The case most commonly quoted is that of Bryophyllum, one of the 

 House-Leek family, whose fleshy leaves may be induced to form buds 

 in the notches of the leaf- 

 margin, by pegging them 

 down on moist soil (Fig. 

 170). These buds root 

 themselves in the soil, 

 and as the leaf decays 

 they remain as substan- 

 tive plants. A similar 

 case occurs in the 

 familiar Cuckoo Flower 

 {Cardamine pratensis). In 

 old plants the radical leaves lie along the surface of the soil, and 

 buds are formed on the upper surface, usually at the forking 

 of the veins. In Malaxis paludosa, a small native swamp Orchid, 

 minute buds appear at the tips of the leaves. Frequently 

 the adventitious bud-formation appears under some stress of 

 circumstances. But this is most evident in those cases where they 

 appear upon roots. For instance, if a Poplar or an Elm be cut down, 

 the root-system is left still alive in the soil. It contains a large supply 

 of plastic material, which it uses in the formation of buds. They 



originate without order from the region 

 of the cambium, and rise above ground 

 as " suckers " (Fig. 171). Fruit trees, 

 such as plums, if severely pruned, also 

 produce similar suckers. These are 

 familiar objects in the vegetable garden, 

 where plums are trained against a 

 wall and pruned. Such adventitious 

 developments are clearly related to a 

 check of the aerial shoot, and may be 

 held to be a method of recovery from it. 

 A special interest attaches to the fact 



Root of Populus alba, bearing adven- . . 



titious buds, which come above ground that vegetative propagation is common 



as suckers. (Reduced.) , . . T . , 



among alpine plants. In them vege- 

 tative buds easily detached replace flower buds. This is seen in 

 Polygonum viviparum, where the lower part of the inflorescence bears 

 as a rule bulbils only, while a variable number of flowers occupy its 

 distal end. The rare Saxifraga cernua seldom flowers in Britain, but 



Fig. 171. 



