NATURE 



265 



THURSDAY, JULY 



23. 1903- 



EXPERIMENTAL MORPHOLOGY. 

 U'illkurliche Entwickelungsdnderungen bei Pflanten. 

 Kin Beitrag zur Physiologic der Entwickelung. By 

 Georg: Klebs. Pp. iv + 166. (Jena : G. Fischer, 

 1903.) Price 4 marks. 

 nPHIS is practically a continuation of Dr. Klebs's well- 

 -L known work " Die Bedingungen der Fortpflanz- 

 ung bei einigen Algen und Pilzen " (Jena, 1896), but 

 whereas that was concerned with the lower organisms 

 the present work deals with phanerogams. Both works 

 are contributions to experimental morphology, the 

 essential feature in both being the performance of a 

 ' ies of experiments skilfully planned so as to dis- 

 >er the nature of the external conditions which lead 

 to certain definite changes of form or function in 

 plants. Englishmen will be glad to see that to Andrew 

 Knight is given the honour of being the founder of 

 this type of work; then follow Hofmeister, Vochting, 

 Sachs, Goebel, Bonnier, &c., nor should it be forgotten 

 that Klebs himself has worked steadily and with bril- 

 liant effect on this line since 18S9. 



Klebs's aim is definitely objective; he seeks to dis- 

 cover facts, without regard to whether the changes 

 arising under given conditions are adaptive. He never- 

 theless allows himself to postulate a certain mechanism 

 in the organism by which he conceives it possible that 

 external conditions produce their effect. His discussion 

 Is interesting, but his terminology seems to us open 

 to criticism, nor does his theory strike us as essential to 

 his aim— the foundation of causal morphology in a 

 purely objective sense. He takes, as an instance, the 

 undifferentiated cells in the growing-point of a plant, 

 in which reside the possibility of developing into organs 

 x;haracteristic of the species. The physical substratum 

 in which this potentiality resides he calls " specific 

 structure." This he assumes to be constant, which 

 implies (we imagine) that under certain definite con- 

 ditions it always develops an identical form, while if the 

 conditions are different the form will be different. 

 Under the heading " conditions " he distinguishes ex- 

 ternal and internal. He retains the term external as 

 being already in common use, though he seems to 

 prefer the expression " directe oder unmittelbare 

 aussere Bedingungen. " These are the various chemic, 

 .thermic, photic, and mechanical influences which act 

 on the organism from its earliest stages. The definition 



of the inner conditions is as follows : 



" Every phenomenon of life occurs within the 

 organism; it is a consequence of the internal condi- 

 tions ruhng at the moment. The quality and quantity 

 of the substances present in the cell, the various kinds 

 ot terments, the physical properties of the protoplasm, 

 c< 11-sap, cell-wall, &c., all these belong to the internal 

 conditions," 



and are *' in the first instance supplied to the individual 

 b\ its origin from a previous generation." 



He also' strongly insists on the internal conditions 



being completely distinct from the specific structure. 



We fail to see that a real distinction between internal 



and external conditions is made good. For instance 



NO. 1760, VOL. 68] 



a naked protoplast placed in a nutrient fluid — a solu- 

 tion of glycerin — is subjected to new external condi- 

 tions. But a vegetable cell treated in the same way 

 takes up glycerin into its cell-sap, and by the above 

 definition the physical properties of the cell-sap are in- 

 ternal conditions. Yet in both cases the change con- 

 sists in exposing protoplasm to a certain solution. Nor 

 again can we clearly distinguish between internal con- 

 ditions and specific potentiality. In a mechanical 

 theory such as Klebs's the " specific structure " must 

 depend on the physical properties of protoplasm, yet 

 these last named are said to be part of the internal 

 conditions. 



All that Klebs proves by his experiments is that a 

 change of external conditions determines a change in 

 the form and physiological processes of the organism. 

 We may conclude from this that the undeveloped tissues 

 are under the rule of changing conditions, but have we 

 a right to draw any other conclusion? Klebs has 

 shown that Saprolegnia grows continuously if supplied 

 with good culture-fluid, but that it at once forms 

 zoosporangia if the culture-fluid is replaced by pure 

 water. The same thing happens if the fungus is left 

 to itself with a limited supply of food, i.e. it forms 

 zoosporangia when the nutriment runs short, thus by 

 its own activity it makes the conditions necessary for 

 zoospore formation. Or, what is another way of 

 putting the matter, the artificial exchange of nutrient 

 fluid for pure water induces zoosporangium-formation 

 because it is an imitati6n of the natural series of 

 changes to which the plant is subject. Klebs does 

 not pretend to say how pure water leads to zoospor- 

 angia being formed; he shows it to be a necessary 

 condition, but the causal connection is absolutely un- 

 known. It possibly always will be so, but it is at least 

 possible to give the problem its proper place among 

 cognate questions, i.e. those relating to reflexes. These 

 are most conveniently studied in the facts of movement, 

 but there is no reason for excluding the facts of ex- 

 perimental morphology. In our opinion, the purely 

 objective method applied to reflexes is incomplete; we 

 differ markedly from Klebs in thinking it impossible to 

 deal fully with the question without taking adaptiveness 

 into account. The fact that a stem bends upwards 

 when deflected from the vertical, depends on some 

 strain or pressure produced in the protoplasm by such 

 deflection. We call this a stimulus, but only because 

 it precedes the act of curving and by endless repetition 

 is associated with that act. What was originally a 

 physical concomitant of a certain position of the plant 

 in relation to the vertical comes to be a stimulus. It 

 may be said that the primeval plant which acquired 

 geotropism did so because there is some unknown but 

 necessary connection between mechanical strain ap- 

 plied to protoplasm and the act of curving upwards. 

 But if so why are essentially similar plants stimulated 

 to downward curvature by a like strain ? Only a vague 

 answer can be made from the objective point of view. 

 From the adaptive point of view there is no difficulty ; 

 any curvature may become associated with any 

 physical change in the protoplasm, upon which it nor- 

 mally and continuously follows. The importance of 

 natural selection is here obvious, for it picks out the 



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