240 MR. S. LE M. MOORE* S STUDIES 



have paracallus as well as callus : while callus alone occurs in the 

 Ash and the Elm. 



4. True callus resists the action of diastatic ferments, but dis- 

 solves in a solution of gum-arabic ; hence there is probably a 

 callolytic ferment in the gum, although efforts to find it have so 

 fap been unsuccessful. 



5. The function of callus and paracallus is to protect the 

 plant by preventing the formation of new shoots under only 

 temporarily favourable conditions of heat, light, or moisture. 



EXPLANATION OF PLATE XX V. 



All figures magnified GOO times. 



Fig. 1. The Fig : a, callus of abaxial sieve-tubes ; b, c, paracallus-masses upon 



the sieve- plates of the inner tubes. 



2. The Ash : sieve-plate plugged with a mass of callus. 



3. Eosa canina: a and b, email paracallus-masses upon sieve-plates; 



p in c, the paracallus-cap, in d a mass common to two sieve- 

 plates. 



4. The Ash : a, before, b, after dissolution of the callus in a solution of 



gum-arabic. 



5 a & b. The same thing, shown in the Fig. 



G. Effect of a gum-arabic solution on the callus of the Vegetable-Marrow : 

 s, the Schleimkopf of contiguous sieve-tubes connected by threads of 

 slime passing through the meshes of the cleared sieve-plate. 



7. The Vegetable-Marrow: a "hedgehog" sieve: the hard paracallus 

 projects from the meshwork in a number of points; p, the mass of 

 paracallus applied to one side of the sieve-plate. 



