454 MYKOLOGISCHE UNTERSUCHUNGEN AUS DEN TROPES. 



of motility, had become enclosed in the clump, a supposition 

 rendered probable by Dr. Hermann's admission that streaming 

 had not yet ceased in the cell mider examination. Moreover, the 

 nature of the movement exhibited by these corpuscles, namely, a 

 changeable plane of rotation but a constant direction, is precisely 

 that of bodies moving passively in a stream of varying volume but 

 fixed direction — such a stream, in fact, as one sees in the cells of 

 the Characem. 



The latter part of the memoir is devoted to a study of the effect 

 of mechanical, thermal, imbibitional, and electrical stimuli upon 

 the streaming movement. Undoubtedly the most valuable portion 

 of this part, and indeed of the whole memoir, is that dealing with 

 electrical stimulation. By a series of delicate experiments, reveal- 

 ing in unmistakable fashion Dr. Hormann's gift as a skilful mani- 

 pulator, phenomena similar to those exhibited by nervous and 

 muscular tissues were obtained with Nitella cells, including a latent 

 period, electrotonus, continued excitation through katelectrotonus, 

 cumulative effect of inefficient stimuli, and negative variation of 

 the current. Dr. Hormann regards the two layers of the proto- 

 plasm as endowed with opposite electrical qualities, the resting 

 layer being positive, the streaming layer negative ; the two layers 

 do not form a continuously electrified surface, but areas electromo- 

 torically effective alternate with others electromotorically in- 

 different, and the whole apparatus may be viewed as forming a 

 series of small galvanic elements ranged side by side. The con- 

 clusion is that a nerve fibre, a muscle fibre, and a Nitella cell agree 

 in possessing an irritable substance, to which is added, in the case 

 of the muscle fibre, a substance giving the phenomenon of con- 

 traction, and in the Nitella cell that of streaming. 



S. M. 



Mykolof/ische Untersuchungen aus den Tropen. Von Dr. Carl 

 HoLTERMANN. Pp. viii, 122, tab. xii. Berlin : Borntraeger. 

 1898. Price 25 Mark. 



The chief value of this painstaking and excellent work is the 

 criticism it furnishes of the Brefeldian system. The author states 

 quite frankly, and I fancy most people will agree with him, that, in 

 spite of the enormous accumulation of material since De Bary's 

 time, we have yet made no advance on his system of classification. 

 His journey to the tropics, extending to fourteen months in Ceylon, 

 Java, Borneo, and the Straits Settlements, has furnished him with 

 a large amount of material for work which engaged him in inter- 

 esting and prolonged cultural experiments. A selection from these 

 results has been made, and published in this well-printed and 

 illustrated memoir. It would take too much space to give anything 

 like an adequate account of the details of his researches, but there 

 are conclusions to which he comes that are of general interest. 

 During the forty years in which the artificial culture of fungi has 

 been practised with success by such masters as De Bary, Tulasne, 

 Brefeld, and others, much, as everyone knows, has been done in 



