314 MENTAL FACULTIES sec. vi 



in a wonderful way of avoiding harmful substances and, 

 traversing tlieir substratum in all directions, of taking up the 

 materials they require. 



" When the internal changes have proceeded so far that 

 the Plasmodia approach the fructifying condition, they are 

 brought by the negative hydrotropism which now sets in 

 from the moist parts of the ground in the forest or wood to 

 the surface, where they creep up various upright objects, 

 often only forming rigid reproductive capsules at some height 

 from the oround. 



"When in autumn the substratum becomes gradually 

 colder, a change which takes place from the surface down- 

 wards, the Plasmodia migrate into deeper regions still having 

 a higher temperature. When the cooling proceeds very 

 gradually, which especially happens in large tan-heaps, the 

 Plasmodia may in their migration reach somewhat consider- 

 able depths, where they then change into sclerotia. To find 

 the sclerotia of ^thalium in winter it is therefore not 

 seldom necessary to search through the mass of tan to a 

 depth of several feet. When the temperature again begins 

 to rise, the sclerotia again germinate, and movement in the 

 opposite direction takes place from the deeper and cooler 

 parts to the upper portions already warmed." 



In the locomotion of the Myxomycetes, then, we see 

 extremely interesting cases of movements due to stimulation. 

 Heliotropism, geotropism, hydrotropism, trophotropism, in 

 general, are stimulus-movements, and ultimately all growth 

 depends on stimulus-movement. It is the most primitive kind 

 of protoplasmic movement. Stimuli in fixed directions and 

 constantly repeated produced, but only secondarily, fixed 

 paths of conduction, and responses of a quite definite kind 

 (reflexes). Thus arose nerves and finally apparatus for 

 storing up stimuli, arose sensation and will — as acquired 

 and inherited faculties. 



