139 



vex surface, the concave surface remained free. This is true of both main 

 and lateral roots and not only under mechanical influences, but also as a 

 result of geotropic and hydrotropic stimuli. Pollock^ has pointed out, in 

 this connection, that twisted roots contain more water in the cells of the 

 convex side than in those of the concave side. 



Noll ascribes this growth of new lateral roots at the point of curvature 

 to a perceptive power of the plant to the formal relations of its own body 

 (Morphaesthesia). This expression may be accepted if by it is understood 

 a mechanical transfer of material resulting from the stimulus of curvature 

 on the affected tissues. The process is similar to the one occurring after 

 direct injury when the cytoplasm has accumulated in the cells adjacent to the 

 wounded surface. Of course laterals are found also on concave parts of 

 twisted roots, but, in such cases, the buds of the laterals were present before 

 the twisting of the mother root had taken place. 



In trees grown in the open the development of lateral roots on the 

 convex side can be of practical advantage, since the plant is thus more firmly 

 anchored and extends over a greater area of soil containing food stuffs, 

 where otherwise the root branches might not have penetrated. But where 

 the whole root ball has only a definitely limited soil space at its disposal, as 

 in potted plants, disadvantages arise w^iich must find expression in the pro- 

 duction of organic substances. We can perceive these disadvantages at 

 once, if M-e observe more closely a pot said to be "root bound." The greatest 

 number of young roots have grown out towards the periphery and been so 

 pressed against the porous sides of the flower pot, that many fibres are 

 broken off when the pot is removed. Part of the root fibres have stuck fast 

 like bands or membranes and have died. The latter circumstance is 

 especially apparent in palms and Dracaenae, in which the dead roots consist 

 only of the stele and the outer bark, which has shivelled up like a papery 

 covering. 



The straining of the roots toward the side of the pot may be attributed 

 to the need of oxygen. Naturally this demand is less easily satisfied as the 

 network of roots fills the ball of earth more closely. To this must be added 

 the secretions of the root itself. Czapek- determined that these secretions 

 may be ascertained in moist air as well as in water cultures. In air saturated 

 with vapor they are frequently observed as drops on the root hairs, the re- 

 sult of a strong internal pressure in the cells. 



Minimum amounts of potassium, calcium, magnesia, sulfuric, hydro- 

 chloric and phosphoric acids are eliminated. Potassium phosphate, causing 

 the well-known reddening of litmus paper, is somewhat more abundant. 

 In regard to acids, Czapek found that the presence of lactic and acetic acids 

 could not be proved, but that, on the contrary, formic acid is found not in- 

 frequently in its potassium salt as a diffusion product of the living, youngest 



1 Pollock, James, The mechanism of root curvature. Botan. Gaz. Chicago, 

 XXIX, 1900. pp. 1 ff. 



2 Czapek, Fr. Zur Lehre von den Wurzelausscheidungen. Jahrb. fiir wiss. 

 Bot. 1896. Vol. 29. Part III. 



