392 



METAMORPHOSIS 



much as the growing point is not itself in contact with the water and can only be 

 indirectly effected by it (p. 339). Similarly, in other cases, as when leaves take 

 on forms adapted to light or to shade, the relationship of light to the growing 

 point enclosed in its scales must be the same in both cases, although a quite 

 different type of leaf is differentiated in the bud of the shaded branch from that 

 of the illuminated one. Experimental investigations on this subject are, how- 

 ever, much required. As NORDHAUSEN (1903) has shown, the characteristic 

 anatomical differences between light- and shade-leaves of the beech are already 

 established in the bud, and the light relations concerned in the unfolding of the 

 bud play only a limited part in the process. If we arrange that the initials of 

 the light-leaf are allowed to develop in the dark, the typical double row of pali- 

 sade-cells (Fig. 115, /) is retained, whilst the shade-leaf retains its own characters, 

 although it be developed in bright sunlight (Fig. 115, 77). The growing point, 

 in this case, undergoes adaptation, and the effect outlasts the stimulus, so that 

 one may readily conceive how hereditary races may in this way come into exist- 

 ence. As a matter of fact, this is not the case in the beech ; further research is 

 needed to show how far the after-effect is continued, whether the branches 

 which have been exposed to light for ten years form 

 leaves of the light-type, after shading, longer than those 

 which have been exposed to intense light for one year. 



Let us ask finally how functional adaptations be- 

 have in regard to inheritance. These naturally cannot 

 be clearly demarcated from those we have just spoken of, 

 and so our knowledge with regard to them is even more 

 limited. The functional adaptations with which we are 

 acquainted are, for the most part, the result of long 

 past influences, and we may well assume that they also 

 first made themselves apparent at the growing point. 

 Where that is not the case, as in VOCHTING'S experi- 

 ments (stem tubers of Boussingaultia, leaf tubers of 

 Oxalis), no transmission can be determined. WINKLER 

 (1902) has recently drawn attention to a case of great 

 interest in this connexion. He observed floral-leaves 

 and styles of a chrysanthemum become green after 

 flowering was over, and exhibit all sorts of anatomical 

 alterations, which were functional adaptations per- 

 mitting assimilation to be carried out. We do not know whether these 

 malformations were transmissible and we are ignorant as to their causes, nor 

 can we assert that they were first operative in the full-grown organ. 



The ideas which we have formed as to the inheritances of acquired charac- 

 ters may be more briefly expressed. We may say that there are no acquired 

 characters in the sense indicated above. The characters do not appear in the 

 soma generally (G5TTE, 1898) but at the growing point, and so far the possibility 

 of their inheritance is granted. In lower organisms, which, as a rule, show no 

 differentiation of somatic and germ plasma, it is quite obvious how the effect 

 of external influences may be inherited (and several observations have been made 

 on the subject), but perhaps no special adaptations may occur in such cases, since 

 the effects produced are of no service to the organism (for literature, see PFEFFER, 

 Phys. II, 242). We have succeeded, by special means, in developing certain 

 races of Bacteria which have permanently lost the power of producing colouring 

 bodies or certain special poisons. We have also been successful, by prolonged 

 culture at high temperatures, in destroying the power of forming spores in 

 various Saccharomycetes. The point which is characteristic in this process is 

 the gradual fixation of the loss ; at a definite high temperature the formation of 

 spores ceases, but the capacity for forming them returns when the temperature is 



Fi. 115. Transverse sec- 

 t ions through leaves of a copper 

 beech, /, primordium of a light- 

 leaf developed in the dark, //, 

 of a shade-leaf developed in a 

 bright light. After NoRD- 

 HAUSEN (1903). 



