Geology and Natural History. 519 



Terletzki's modification of the earlier methods. In the case of 

 succulent plants it was found advantageous to dip the parts to be 

 sectioned in boiling water and then harden them in absolute alco- 

 hol As a coloring agent Hoffmann's aniline blue was chiefly 

 employed, but the combination of this staining agent with picric 

 acid, so highly recommended by Gardiner, was found to give too 

 faint a tint— an experience we believe, which has been shared by 

 others. Especial difficulty was found in coloring, where the cell- 

 walls were cutinized, and in such cases a strong solution of methyl- 

 violet gave the most satisfactory results. As a mounting agent 

 glycerine proved useless, while Damar and Canada balsam are 

 recommended. 



In a systematically arranged list the author enumerates some 

 sixty species, from the Hepaticoe upward, which have been inves- 

 tigated by him, and indicates in each case the elements between 

 which protoplasmic threads were observed. As the tissues in 

 and between which the continuity of protoplasm has been de- 

 tected embrace nearly every kind of histological element, the con- 

 clusion — already stated by others upon a less secure basis of 

 observation — is drawn that all the elements in the higher plants 

 are so connected. A single exception, however, is made in the 

 case of the guard-cells of the stomata, the walls of which accord- 

 ing to Kienitz-Gerloff are entirely free from perforating threads. 



The morphology and origin of the threads are excellently dis- 

 cussed and the phenomena observed are well illustrated in a num- 

 ber of figures. Details of course cannot be given here. It may 

 be mentioned that the spindle-shaped enlargements of the proto- 

 plasmic threads, so frequently observed near their middle but not 

 altogether confined to that region, are plausibly explained on the 

 ground that some of the lamellae of the cell-walls, notably those 

 near the middle, are much less strongly swollen than others by 

 such reagents as sulphuric acid, and therefore exert less pressure 

 upon the penetrating threads. The protoplasm accordingly re- 

 mains in greater quantity at these points. Our attention is also 

 called to the fact that the connecting threads as they exist in 

 nature, are doubtless much larger than they appear after treat- 

 ment with reagents employed to bring them into view. Both the 

 morphological descriptions and accompanying figures render 

 Russow's theory, just mentioned, very doubtful. Its disproof 

 however is not altogether conclusive. 



Of especial interest is the treatment of the physiological aspect 

 of the continuity of protoplasm, and here Kienitz-Gerloff* favors 

 strongly the theory of Kohl and Wortmann, that a transference 

 of protoplasm and the substances it contains really takes place 

 from cell to cell by means of the threads. This view has been 

 opposed by various observers, most recently by Noll and Zimmer- 

 mann, who are inclined to consider the function of the continuity 

 rather the communication of shock or impulse. Of the several 

 very plausible reasons which Kienitz-Gerloff gives lor believing 

 that a transference of matter is effected by the structures in 



