108 ANATOMY AND PHYSIOLOGY OF 



on the roots of a large number of trees (e. g.^ Poplars, Wild Cherries, 

 Plums, &a), as well as on the leaves of many plants {e, g., As- 

 pidiv7}i bulbiferuTYij Malaxis jpaludosa^ and Bryojphyllurn call-' , 

 cinum). 



The pollarding of a plant frequently causes the development of 

 shoots. The formation of roots generally takes place readily 

 when the descending sap is arrested anywhere in its downward 

 course by cutting through the baik, especially when, at the same 

 time, light is excluded from the wounded spot, and this kept 

 moist. In this case, the roots break out in most plants from the 

 thickening which is formed at the upper border of the wound. 

 On the other hand, the plant is caused to form leaf-buds in un- 

 usual places when the whole of the leafy part is cut off; for then 

 leaf-buds are formed beneath the bark, both on the lower part of 

 the stem and on the roots, breaking through the bark, and grow- 

 ing up into stems Most Dicotyledonous trees possess this power 

 until they have attained too great an age, but most of the Coni- 

 feise are devoid of it. This capability of foiming leaf-buds is so 

 great in many plants, that every fragment of the root may be 

 used for raising new plants from it, — for example, in the horse- 

 radish, Madura aurantic^, &c. 



It is most difficult to induce the formation of buds on the 

 leaves. Detached leaves have very great tendency to form roots, 

 when they are placed in moist earth ; they afford, under such cir- 

 cumstances, the peculiar example of a plant which fully exercises 

 the functions of nutrition, but is altogether incapable of growth. 

 Such rooted leaves sometimes attain an age far exceeding their 

 usual period of existence; thus Knight, for example, saw the 

 leaves of Mentha piperita, which he had caused to produce roots, 

 maintain themselves fresla for more than a year, and assume 

 almost the aspect of evergreen leaves (Knight, " Selection from 

 the Physiol Papers/' 270). Growth into a new plant is only 

 possible in such a rooted leaf when it developes a leaf-bud ; in 

 general, this does not readily happen. There are plants, it is 

 true, as already mentioned, on the leaves of which leaf-buds are 

 regularly developed ; and a considerable number of plants have 

 been noticed, on which buds had formed accidentally, on par- 

 ticular leaves, still connected with the plant, e. g., Drosera, For- 

 tulaca, Gardaonine pratensis^ Glechoma hederacea, &c. ; but, on 

 the whole, these examples are rare. Buds are most readily formed 

 on detached leaves when these have a fleshy consistence ; their 

 development has been observed in particular on the bulb scales of 

 Eiicorwis regia^ Lilium caoididum, Hyacmfmis, Scilla mari- 

 tima, on the leaves of Ormthogalum thyrsoides, &c. ; moreover, 

 not unfrequently on the leaves of different species of Crassula 

 and Aloe, Buds are formed much less readily than on such suc- 

 culent leaves, on leathery leaves,— for example, of Gitms, Aucuha, 

 Hoya camosa, Ficus eladka, TheoihuisP^, &a, although these 



