179 



side and then on (lie other. The reason of these changes in the 

 speed of llie growth is unknown, bui, while a renewed research 

 into these movements is highly desirable, it may be taken as fairly 

 certain that, althougii all appai-ently similar, they are not so in 

 reality, since they are evidently not all governed by the same 

 stimnli. The influence of gravitation, for instance, can be demonstrated 

 in many of them, so that for this reason and also because the 

 movements depend entirely upon longitudinal growth, there is every 

 reason to assume that statocysts are also present in these organs. 

 With respect to the place where they occur in leaves in general, 

 not much is known, and it would therefore be useless to make 

 further premises i-egarding the shifting of the static apparatus before 

 sutHicient data on this point have been obtained. 



Some movements, however, might already be explained in a similar 

 way as above; so, for instance, the movements of the leaves in 

 the unfolding buds of Aesculus; in the bud, and also as soon as if 

 opens, the petiole and leaflets stand vertically upright, after which 

 the leaflets make a downward bend of 180° at the joint ishifiing 

 of the a|)paratus from the basal to the apical transverse wall); 

 finally the leaflets, as well as the petioles, take up an almost hori- 

 zontal position (shifting of the apparatus in both to the undermost 

 longitudinal wall). 



In connection with the above 1 may refer to the very important 

 though apparently almost totally forgotten observations of HorMEisTER '), 

 from which it would seem that the lateral growth of the leaves in 

 the bud is frequently influenced by their vertical position so that 

 the half of the leaf pointing upwards in the bud will grow faster 

 than that pointing downwards. If these observations be correct they 

 would form a further indication that statocysts are also present in 

 the leaves and would thus be able to exercise an influence upon 

 the growth of the cells. This would agree with ray view, expressed 

 above, namely that the static apparatus also governs the normal 

 growth in length. We shall return later to the consideration of the 

 influence of gravitation upon the normal position of the leaves, as this 

 also should be connected with the influence of the static apparatus 

 (page 184). 



b. The position of the static apparatus is altered by external 

 influences. 



Sometimes an external influence leads to a change in the position 

 of organs, as, for instance, amputation of the main-axis. 



') Allgemeine Moi-phologie der Gewachse. 1868, § 23. 



