May 6, 1897 J 



NATURE 



morphological) peculiarities of the race, a good deal of 

 initial specialisation must first have occurred ; this will 

 be equally true, whatever view we choose to adopt as to 

 the homologous or antithetic nature of the origin of the 

 process itself. 



In the highest forms, we are very far from being able 

 to answer the initial question as to what it is which 



luses the organism to enter on the reproductive as 



pposed to the vegetative phase, although as regards 

 the actual phenomena of reproduction itself, we can 

 fairly accurately predict the course which the process 

 will take. But this is merely because it is far less directly 

 aflfected by the action of the environment than are the 

 functions of nutrition and growth. Nevertheless, al- 

 though the empirical facts may be easier to glean, their 

 very invariability opposes perhaps the strongest obstacle 

 to our grasping the nature of the chain of causes of 

 which they themselves merely constitute the terminal 

 expression. 



But in the lower forms, including most algcX^ and fungi, 

 the physiological differentiation has not progressed far 

 enough to effect such an adjusted state of organisation as 

 will commonly respond in an identical manner to the 

 action of any stimulus whatever that may happen to be able 

 to excite it at all, for they will either grow vegetatively, 

 or they will reproduce themselves sexually or asexually, 

 according as the exigencies of the environment may 

 •demand. It is to them, therefore, that we look to find 

 the clue that shall enable us to penetrate the dense 

 obscurity which at present veils the whole subject. 



But although reproduction and the conditions which 

 affect it has long afforded a favourite theme for specula- 

 tion, its investigation from a scientific and experimental 

 standpoint has been surprisingly neglected. A certain 

 amount of scattered knowledge has been gathered, owing 

 largely to the efforts of gardeners and others practically 

 interested in the solutions of the problems with which we 

 are here concerned, but for definite attempts at thorough 

 investigation by means of inquiries properly formulated 

 and vigorously pursued we have looked, until lately, 

 almost in vain. 



Prof. Klebs, then, is the more deserving of the con- 

 gratulations of all who are interested in these difficult 

 problems on account of the admirable manner in which 

 he has conceived and conducted his elaborate and 

 beautiful series of experiments which are described in 

 the volume before us. For his results conclusively prove 

 that these recondite functions of protoplasm are as 

 amenable to experimental treatment, if approached in a 

 suitable manner, as are those of irritability or of nutrition. 

 It is difficult at present to estimate the exact limitation of 

 Dr. Klebs' methods or the general value of his conclu- 

 sions, but the results as yet obtained are truly surprising. 

 Instead of uncertainty, we find definite reactions on the 

 part of the organism to varied external conditions, and 

 the present writer can testify to the accuracy of the 

 author's statements in a number of crucial instances. 



Of course it is impossible here to give more than a 

 mere sketch of the enormous mass of detailed observation 

 piled up, in a rather unwieldy fashion it must be con- 

 fessed, in Prof. Klebs' book, but a few typical facts will 

 serve to indicate the general drift both of his methods 

 and his results. 



NO. 1436, VOL. 56] 



A somewhat large proportion of the entire number of 

 pages is devoted to an account of Vaiichcria tcrrcs(ris, of 

 which the author recognises three varieties which showed 

 differences, sometimes slight, sometimes rather striking in 

 the respective manner in which they responded to similar 

 stimuli, but for the details the original treatise may be 

 consulted. The plants were investigated with a view of 

 determining the conditions which govern the formation 

 of the non-sexual zoospores and the sexual gametes re- 

 spectively, and especial attention was directed to the 

 influence of heat, light, medium of cultivation, organic 

 or inorganic food, and so forth. Dealing with the alga 

 at first from the point of view of its zoospore-formation, 

 a large number of striking facts was elicited. It must 

 be premised that Vaucheria only forms zoospores when 

 it is growing immersed in water ; but, as will be seen, 

 this is only a very small part of the story, since the con- 

 ditions to which it happens to have been previously exposed 

 when growing in terrestrial stations have an important 

 influence in determining whether, on immersion, these 

 bodies shall or shall not be produced. For example, if 

 plants which have been grown on soil in a damp atmo- 

 sphere be suddenly submerged in water, zoospores are 

 copiously produced within a short time, and this is 

 especially the case if the submergence be accompanied 

 by a darkening of the culture, whereas if a dry earth 

 culture be similarly treated zoospores may perhaps not 

 be produced at all. They are, in any case, only formed 

 in the upright filaments, such as may be seen rising up 

 abundantly in any specimens cultivated in damp air. 

 Furthermore, the change from an aerial to an aquatic 

 medium must be a sudden one. A gradual submergence 

 produces no effect, and this fact gives us a probable clue 

 to the cause of the failure of plants which have previously 

 been kept dry to form zoospores after immersion. Under 

 these circumstances the erect filaments are not produced, 

 and by the time they do appear in the water culture, 

 the stimulating effect of the change of medium seems to 

 have ceased to operate. 



As regards the action of changes of temperature, it 

 was found that in general a rise of a few degrees pro- 

 voked the formation of the zoospores, especially when 

 the plants were grown at low temperatures, but that the 

 converse process of cooling was without effect. The in- 

 teresting discovery was made, that whereas the lowest 

 normal limit at which the plants could thrive and retain 

 their sensitivity was about 3^ C, this could be consider- 

 ably lowered by gradually accustoming the plants to 

 increased cold, and that under these circumstances they 

 still responded to an increase of warmth in the usual 

 manner, i.e. by the production of a crop of zoospores. 



Much interesting matter is to be found in the pages 

 devoted to the consideration of other conditions affecting 

 the production of zoospores ; but in this place we will 

 content ourselves with indicating some of the more im- 

 portant ones connected with the influence of light. In 

 water-cultures grown under healthy conditions, zoospores 

 are readily produced on the withdrawal or diminution 

 of light. It turns out that plants exposed to blue light 

 behave as in the dark, i.e. they form zoospores, but that 

 in yellow rays these bodies are not produced. It might 

 seem natural, at first sight, to connect this peculiarity 

 in some way with the assimilatory functions which are 



