goebel's investigations on scale-leaves, etc. 507 



plenium, Anemone hepatica, and other species of Anemone, may here be mentioned. 

 In all these cases the subterranean and sometimes succulent scales have arisen 

 by the further development of the foliar base, while the lamina, though still more 

 or less evident, is arrested. 



That, so far as these scale-structures are concerned, it is actually a matter 

 of correlation of growth, Goebel has experimentally demonstrated in the case of 

 Prunus padus, among others. The growth of this tree proceeds as follows. In the 

 spring the axillary buds of the shoots of the previous year become unfolded and 

 again form axillary buds in their turn : these produce in the first place bud-scales, 

 and pass through the period of rest during the summer and following winter 

 enveloped in these. The bud-scales which thus arise in the spring come into 

 existence in Prunus padus by the vigorous development of the foliar base, which 

 bears above indications of not only the proper lamina of the leaf but also of 

 two stipules, all, however, very small and only recognisable by means of the 

 microscope. 



On the 14th of April a number of growing shoots and young plants of Prunus 

 padus were partly deprived of leaves, and partly lopped at the apex; that is, the 

 terminal buds were removed. On the loth of May the result was that the axillary 

 buds which should normally unfold only in the next spring had commenced to put 

 forth shoots, and vigorous normal leaf-shoots were subsequently developed from 

 them. Apart from other results of this experiment, it teaches that the leaves impelled 

 to further growth immediately after their origin did not become developed in the 

 usual manner into bud-scales, but assumed the form of ordinary foliage-leaves. 

 The rudiments of foliage-leaves, which when the shoot is left to itself have their 

 laminae arrested and develope their foliar base as bud-scales, here developed into 

 normal foliage-leaves; and this because the development of the leaves of the mother- 

 shoot formed in rudiment in the previous year had been prevented early, by 

 taking away or lopping the apex. Thus the nutritive materials necessary to the 

 development of true foliage-leaves were able to reach these young leaf-rudiments, 

 which, as a rule, develope as scales — or in other words, the growth of the foliage- 

 leaves of a shoot of Prunus padus which is putting forth leaves prevents the lateral 

 shoots which simultaneously arise in the axils of its leaves from completing the 

 development of their foliage-leaves also. This demonstrates the correlation of the 

 two, and the case is similar in many other plants. This was experimentally 

 confirmed by Goebel in the case of the Horse-chestnut, and in Maples, Roses, 

 Syringas, and Oaks. Into Goebel's more involved researches, and those made on 

 plants which may be less known to the reader, we will not here enter. 



The complications which make their appearance in the experimental investiga- 

 tion of the correlations of growth are chiefly due to the fact, that with the altered 

 growth of an organ all its reactions towards the environment also become changed : 

 this shows at the same time, as I stated in the first lectures, that the true physio- 

 logical nature of an organ is to be sought not so much in its outward form and 

 anatomically visible structure, as in its irritability or capability of reaction. Even 

 in the first-named example of the potato, and in the substitution of the removed 

 apex of the stem of trees, it is clear enough how, with the change of growth 

 by means of interference with the correlations, the geotropism also — i.e. the 



