1022 SUMMARY OF CURRENT RESEARCHES RELATING TO 



" Sclerotioids " of Potato.* — Mr. A. S. Wilson finds in the leaves 

 of diseased potatoes sclerotium-like bodies composed partly of proto- 

 plasm and partly of calcium oxalate, which he believes to be connected 

 with the disease, the protoplasm not being found within the cells, 

 but in the intercellular spaces through which the mycelium of the 

 Phytophthora passes, consisting, therefore, probably of the remains of 

 the fungus. Mr. G. Murray, on the contrary, maintains that they are 

 merely mechanical concretions of the protoplasm of the cells of the 

 leaf with calcium oxalate. 



Laticiferous Vessels. f — Prof. S. Schwendener has investigated 

 the laticiferous vessels of a number of plants, with the view specially 

 of determining the following points : — the special conditions which 

 cause the occasional very considerable thickening of their walls ; the 

 physical properties of their walls ; and the cause of the movements 

 in the latex. 



The thickness of the walls was not found to be proportional to the 

 age of the vessels ; nor is there any simple arithmetical relationship 

 between the thickness of the walls and the diameter of the tubes. 

 The thick-walled tubes frequently bound intercellular spaces full of 

 air, while those with thin walls permeate the parenchyma which is 

 without interstices. The object of the thickness appears to be to 

 present a resistance to the pressure of the contents, which may 

 amount to several atmospheres. This is shown by the fact that if 

 drops of desiccated latex, which are frequently found in the tubes, 

 are dissolved in ether, the diameter of the tubes diminishes 4 or 5 per 

 cent., while their walls increase 50 per cent, or more in thickness. 

 It follows also from this observation that the inner lamellse of the 

 walls undergo greater tension from the contents than the outer 

 lamellae ; the former show remarkable tenacity and elasticity, and 

 can be stretched at least 10 or 15 per cent, in the direction of their 

 length. 



This elastic tension of the walls may obviously occasion move- 

 ments in the contents of the tubes ; such a movement towards the 

 points of least pressure can be observed in the latex of seedlings of 

 Chelidonium majus ; for example, in the apex of the tap-root. Varia- 

 tions of pressure are brought about in the living plant by the elonga- 

 tion of the laticiferous tubes in the apical growth of the organ, and 

 by changes in the composition of the latex. The author was able 

 also to demonstrate a mass-movement of the latex by observation of 

 the form and distribution of the solid substances found in it, especially 

 starch-grains. Even unseptated laticiferous tubes may become closed 

 by the pressure of the adjacent parenchyma, or by the formation of 

 walls within the tubes. 



With regard to substances excreted in the latex, it was found to be 

 considerably more watery in withered or half-withered fig-leaves, in 

 mulberry-shoots in the hibernating state, in roots of Tragopogon 

 from which the leaves had been removed, in specimens of Lactuca 



* Proc. R. Hort. Soc, 1885, March 10. See Journ. of Bot., xxiii. (1885) p. 74. 

 t SB. K. Preuss. Akad. Wiss., 1885, pp. 323-36 (1 pi.). 



