412 ME. F. DABWIN ON THE 



by gravitation ; since the relation between the chief direction of 

 growth and the force of gravity is exactly reversed in the above 

 cases when compared with the rooting of pendent bramble- 

 branches. It seems only explicable according to Vochting's law, 

 that there is a tendency to the production of organs in certain 

 morphological positions, a tendency in large measure independent 

 of external forces. This conclusion is supported by the results of 

 the following experiments : — 



Two Brambles, which were growing horizontally, or slightly 

 above the horizon, were (Sept. 14 and 23) tied apex upwards to 

 vertical sticks. They were at first wrapped up in yew-branches ; 

 but as this did not seem to give the necessary amount of dampness 

 nor to exclude enough light, they were subsequently covered up 

 with damp moss, which was wrapped round with waterproof cloth. 

 At one time both of them bent over so as to become nearly hori- 

 zontal, and were then tied up again so as to remain vertical. They 

 remained in this position until Nov. 16. It was then feared that 

 the cold weather would prevent the development of the rudi- 

 mentary roots, which could just be distinguished, and they were 

 accordingly freed from their connexion with the parent plant, 

 the apex remaining uninjured. They were placed in damp air 

 and kept dark, the cut ends being immersed in water. Under these 

 conditions, in an ordinary room, a root, about a centimetre in 

 length, was (Nov. 22) developed at the apex of one of them ; and 

 by Nov. 26 the terminal 4 cm. was studded over with roots break- 

 ing through the epidermis. The growth at the apex of the branch 

 seemed to be checked, and several minute root-bearing shoots 

 were developed in the axils of the terminal leaves. 



In concluding that there is a morphological force in the Bramble 

 which leads to the production of roots at the apical end of the 

 branches, I am far from denying that gravitation has an effect on 

 their production. At the same time that the above-described expe- 

 riment was made, two other Brambles were tied (Sept. 14) apex 

 downwards to vertical sticks, and were covered with moss and yew- 

 branches. On Oct. 14th one of them had produced a number of 

 strong roots at its apex, the other one had grown out below the 

 mass of moss &c. and had not rooted. This fact makes me sus- 

 pect that gravitation is an accessory stimulus for the production 

 of roots at the apex. This question I hope to decide next 

 autumn. 



