SCIENTIFIC SUMMARY. 
75 
The theory which Sachs has brought forward in his paper on Staff 
und Form der Pflanzenorgane * is entirely opposed to that of Vochting. 
Sachs conceives that Vochting’s ‘morphological force’ is not a hereditary 
tendency, but a tendency produced by the action of external forces during 
the growth of the formative cells. Thus Sachs believes the force of 
gravity acting on the developing cells of an organ produces on it a pre- 
disposition or enduring impulse, which manifests itself in the results which 
Vochting ascribes to a hereditary force. The mode in which Sachs believes 
gravitation to act is interesting, not only in itself, but also as a modification 
of a theory of Du Hamel’s. It is assumed that difference of material is a 
necessary concomitant of difference of form, and that accordingly the 
materials from which roots are formed are chemically (used in a qualified 
sense) different from those which supply the branches. Sachs’ theory 
supposes that the growth of roots or buds at a given place will be determined 
by the distribution of the root- and branch-forming materials, and that the 
distribution of these materials is regulated by the force of gravity. The 
root material is in a certain sense geotropic, and flows downwards, the branch 
material having the opposite tendency. But they are not supposed to be 
simply geotropic ; the tendency of the root-material to flow to the base of a 
branch is carried on after the branch has been made into a cutting, and hung 
upside down, so that the root material flows upwards towards the base of 
the cutting, because that end was originally downwards, and vice versa with 
regard to the branch-forming matter. 
The observations on the bramble, which form the subject of the 
present paper were carried out with the object of deciding, for a particular 
case, whether the growth was determined by a morphological force, or by 
the after-effect of gravitation. 
The long sterile shoots of the bramble are well known to possess the power 
of rooting at their ends. The terminal bud is thus protected during the 
winter, and the store- of nutriment contained in the club-like thickened end 
of the branch forms a starting-point for new growth in the spring. It is 
commonly the long pendent branches growing vertically downwards that 
reach the ground and form roots. It might, therefore, be supposed that 
gravitation determines their growth at the lower end of the branch, just as, 
in a cutting made from an erect willow-branch, the roots grow at what was 
originally the lower end. But observations made on brambles under certain 
circumstances show that this is not the case. When brambles grow on a 
steep bank, the majority of the branches grow down-hill at once, or else 
straggle more or less horizontally along the bank, and finally turn down- 
wards. But a certain number of branches grow uphill, and some of these 
take root at the apex. When, therefore, we find on the same individual 
plant some branches forming roots at the physically lower, and others at 
the upper end, we may feel sure that the distribution o root-growth in the 
bramble is not determined by gravitation or its after effect. We must 
believe that there is a morphologically directed impulse which tends to the 
production of roots at the apex of the branch, whether the direction of its 
growth has been upwards or downwards. It is true that in the observed 
* Arbeiten des Bot. Inst. Wurzburg, 1830, p. 452. 
