BUDS ON ROOTS. 25 



cups are produced, within which thallidia are continuously developed in the manner 

 shown in figs. 196 1- ^> ^' *• ^' «■ '■ ^. 



The formation of these brood-bodies by Lichens and Mosses may be induced by 

 wounds or mutilations afiecting the plants in question; but the stimulus is not 

 here susceptible of being so clearly and surely inferred from its effects — and 

 perhaps has hardly yet been so carefully investigated — as in the case of trees, 

 shrubs, and herbs, which, being planted on a large scale, have afforded experience 

 for centuries with the result that the practice of inducing the formation of buds 

 by mutilation and of using them for the purpose of artificial propagation is 

 extremely common in cultivation. Parasitic thallophytes receive an evident 

 stimulus to the formation of brood-bodies upon the death of their hosts. As 

 long as the host-plant is healthy and vigorous the parasites keep their hyphse 

 and suckers buried within the nutrient tissue. They there consume all there is 

 to consume, increase in size, and thread their way through wood and green tissue 

 in ever-widening circles — but without ever forming brood-bodies. Not until the 

 host is quite exhausted and languishing at death's-door does the parasite, to avoid 

 the danger of perishing with its foster-parent, provide for its departure from the 

 ruin, and it is then in the form of brood- bodies that it escapes from the tissue 

 it has ravaged. Here and there some of the tubular cells grow quickly from the 

 interior of the dying tissue of the host-plant and emerge to the surface through 

 stomata or rotten cell-walls. All the substance contained in the cells of the 

 parasite becomes concentrated at these new foci of formative activity, and here 

 masses of spores and thallidia are developed and abstricted at the very points 

 where most extensive distribution is rendered possible by currents of air and 

 water. Thus, the parasite is resolved into a number of brood-bodies and abandons 

 the mansion which it has brought to destruction. 



BUDS ON" EOOTS. 



Just in front of the house in which I am writing there used to stand years 

 ago a great Aspen. The tree was felled, the axe being laid so close to the earth 

 that only a stump projecting a few centimetres above ground was left. In the 

 following spring the stump became the centre of quite a grove of Aspens, slender 

 shoots having pushed through the grass over a large circular area round the 

 stump. At first the shoots appeared one by one, then by dozens, and at last 

 by hundreds at a time. They grew up into trees, and now, instead of the single 

 Aspen, there is a little wood composed of trees which have not sprung from seed, 

 but from the subterranean roots of the felled Aspen. Before the old tree had 

 been deprived of its trunk and foliage its underground roots produced lateral 

 roots only, which grew in a plane beneath and parallel to the surface, and 

 continued to spread so long as they did not encounter any insuperable obstacle. 

 Suddenly there was a change ^n the processes going on in this root; its formative 

 energy was no longer devoted to the development of lateral roots, but was directed 



