SECT. II ■ PHYSIOLOGY 291 



Fluctuating variations are quantitative deviations from a mean type 

 which can be counted, weighed, or measured. They appear to be deter- 

 mined by the external conditions of growth which similarly fluctuate 

 around a mean value, and they can be to a certain degree fixed or even 

 increased by careful selection. Thus, for instance, the amount of sugar 

 in the sugar-beets has been considerably increased by selection. On 

 selection ceasing this artificially niaintainjed variation disappears, and 

 this would be the case in nature. In contrast to these fluctuating 

 variations the mutations are larger or smaller deviations from the 

 type which suddenly, not gradually, appear from unknown causes, 

 and possess inheritable characters. Such mutations have been most 

 thoroughly studied by DE Vries in Oenothera LamarcMuna. Typical 

 examples are also afforded by many forms which have spontaneously 

 appeared in gardens, and have proved the starting point for valuable 

 cultivated forms. Examples are Chelidonimn laciniuhim, which arose 

 in 1590 in a Heidelbei'g garden, and Capsella Heegeri, Solms, which 

 appeared at Landau. 



It is hardly a matter of doubt that new sub-species (petites espkes, 

 of which Jordan has described over 200 in Draha verna) have arisen 

 by such sudden mutations. More distinct species may develop from 

 these, partly by the occurrence of further mutations, and partly 

 by the dying out of the intermediate forms and the persistence of 

 the extreme forms. Since those organisms which do not possess 

 sexual reproduction are also differentiated into genera and species, 

 the occurrence of mutations cannot be confined to digenic reproduc- 

 tion. Bad-variations have also been frequently observed to arise 

 (cp. p. 284). 



Sub-Section "III. 



Movement 



Phenomena of movements are met with in the living plant not less 

 generally than those of metabolism and development. jNIetabolism is 

 associated with a continual movement of the raw food-materials, which 

 are absorbed, and of the elaborated assimilates and excreted sub- 

 stances. These movements cannot be directly observed, but are not 

 less certainly established ; they have already been dealt with. In 

 addition there exist a number of visible alterations of position exhibited 

 either by the whole plant or by its several oi'gans ; these movements 

 are, it is true, often very slow but sometimes are quite sudden. 



I. Survey of the Various Kinds of Movement 



Protoplasm itself is capable of different movements. Naked 

 protoplasmic bodies almost always show slow movements resulting in 



