250 BOOKS AND CURRENT LITERATURE 



Root Tubercles. — Spratt 1 has investigated the structure of root 

 tubercles in several legumes and non-legumes, among the latter, Cycas, 

 Podocarpus, Alnas and Ceanothus. In all Bacillus radicicola enters 

 through the root hairs. The origin of the nodule, however, is different 

 in the two groups. In legumes, the infection is followed by hyper- 

 trophy of the cortex of the invaded root, which results in a mass of tis- 

 sue becoming externally visible. At the base of this mass vascular ele- 

 ments appear which become continuous with the stele of the root and 

 develop superficially in relation to the bacteria-containing cells. Even- 

 tually the tubercle breaks through the root parenchyma. Modification 

 of the peripheral meristem of the tubercle often occurs, so that the sur- 

 face may be rough or branched instead of smooth and roundish. In 

 Robinia, Sophora and Acacia, the tubercles are perennial and develop 

 from the phellogen a protective tissue. 



In non-legumes, the nodule is a modified lateral root which becomes 

 infected with Bacillus radicicola while traversing the cortical paren- 

 chyma of the parent root. Since the plerome of the lateral root is 

 already differentiated the stele remains unaffected to continue its cen- 

 tral position, — a position just the reverse of that occupied by the vas- 

 cular strands in the nodules of legumes. 



The cell sap is said to have a marked influence on the invading bac- 

 teria, determining the ability of the latter to enter and the extent to 

 which infection threads may be produced. — J. G. Brown. 



Penetration of Bean Cuticle by Colletotrichum Lindemuthi- 

 anum. — That Colletotrichum Lindemuthianum penetrates the cuticle of 

 the host in a purely mechanical way and is unable to gain entrance by 

 disorganizing the cuticular layer, is claimed by Dey. 2 An appressorium 

 is formed by the germ tube, which is attached to the surface of the host 

 by a mucilaginous envelope. The appressorium subsequently sends 

 out from its surface a peg-shaped infection hypha which pushes through 

 the cuticle of the host in the same manner exhibited by Botrytis 

 cinerea. — J. G. Brown. 



1 Spratt, Ethel R.,' A Comparative Account of the Root-nodules of the 

 Leguminosae. Ann. Bot., 33, pp. 189-200. 1919. 



2 Dey, P. K., Studies in the Physiology of Parasitism. Ann. Bot 33, pp, 

 305-312. 1919. 



