SUPPLEMENT 103 



Internal conditions are, however, very variable, and the environment, 

 inasmuch as it induces changes in them, has certainly only an indirect influence 

 on the development of the plant. 



We cannot accept this conception of KLEBS'S because we look at the phe- 

 nomena from an essentially different point of view. It appears to us that 

 KLEBS has advanced no proof whatever that a cell really grows because 

 certain materials, such as proteid, carbohydrates, and enzymes, are present 

 or absent. On the contrary, we believe that it is not the presence or absence 

 of a substance that determines the activity of protoplasm, but that the 

 presence or absence is determined by the protoplasm. But what we generally 

 understand by protoplasm cannot be identical with that which carries these 

 potentialities. Only a part of it, to which has been given the name of idioplasm, 

 can be the bearer of such potentialities, and what is left over, cell-sap, cell-wall, 

 &c., might be an internal condition of the idioplasm. But ' internal conditions ' 

 of this kind can scarcely be separated from specific structure, as we shall attempt 

 to show by an example. According to KLEBS the polarity of plants is due to 

 external factors or to internal conditions dependent on them. We have seen 

 that no proof has been advanced in support of this view, but we have also 

 pointed out that, even if it were so, we could not assume that polarity should 

 make its appearance without a distinct capacity on the part of the plant to 

 exhibit a polar structure. This capacity must, however, be specific, and 

 dependent, as KLEBS says, on specific structure, for one cannot regard a higher 

 plant as apolar. The oosperm of a willow divides into two polar segments, 

 and though certain internal conditions may be the determining factors which 

 settle which region of the oosperm must become one segment and which the 

 other, one cannot regard these conditions as the agents in first inducing polarity. 

 It would have to be shown that the plant, in the absence of these conditions, 

 did not grow at all, or grew as an apolar sphere. 



Further, it appears to us to militate against KLEBS'S conception that his 

 whole efforts are all the same directed towards destroying more and more the 

 boundaries between specific structure and internal conditions. If KLEBS 

 considers that by the appropriate action of external or internal conditions 

 everything may be explained, why does he leave out potentialities, and regard 

 them as invariably of service to the plant, even when a characteristic crops up, 

 not noticed previously, but constant from the moment of its origin (compare 

 ' Mutations ', Lect. XXX) ? 



We dissent from the view that distinguishes between internal conditions 

 and specific structure, because the view is quite untenable. Further, it is impos- 

 sible to draw a hard and fast line between internal and external factors. Still, 

 if we establish merely these two categories, we have only one line of distinction 

 to draw, not two, as KLEBS has. Following PFEFFER, we regard as internal 

 or autonomous causes of plant form, all factors which affect the development 

 of the plant under constant external conditions, and amongst internal 

 factors we naturally include also correlations. Certainly we are far from 

 comparing these internal causes with the unchangeable causes of formation. 

 It must always be our task to analyse, as far as may be, these internal 

 causes. That we shall be able to do so but to a limited extent, renders it, 

 unfortunately, often impossible for us to obtain a closer insight into the 

 problems of development. 



340, 11. 47-8, for Even plants, which . . . Siphonaceae) read Plants which 

 increase by means of a growing point, no matter whether it consists of a part 

 of a cell (as in the Siphoneae) or of many cells, 



341, 1. 21, for a very read an even more 



