208 COOK 



methods by which organisms are able to place themselves in 

 more advantageous relations to their environment, and to man- 

 ifest a power of choice with reference to external circumstances. 

 Even among the simplest types of organic structure this faculty 

 is definitely in evidence. The slime-moulds (myxomycetes) pass 

 the vegetative period of their existence in rotten wood or other 

 decaying vegetable matter. By simple amoeboid movements 

 the naked, softly slimy protoplasm, of which these primitive 

 organisms consist, is able to creep out at maturity to an exposed 

 surface before giving up its water and separating itself into dry, 

 wind-blown spores. 



To better accomplish the work of dissemination many of the 

 myxomycetes have the hereditary talent or instinct to subdivide 

 their colony into small masses, each of which builds itself a 

 stalk to climb upon. There is then built out from this stalk a 

 network of threads to hold the spores so that they can be sifted 

 out and scattered gradually by the wind, instead of falling at 

 once to the ground. The stalk-building myxomycetes do not 

 work, however, by any arbitrary or merely mechanical stand- 

 ards. When the surface of the decaying log over which they 

 have spread themselves at maturity is uneven, so that a part of 

 them must stand in wet depressions or chinks of the bark, these 

 have longer stems than the others. In some species only those 

 in the wet situations will have stems, while those in exposed 

 places will remain seated directly on the substratum. 



The building of the stem and the climbing up are not two dif- 

 ferent adaptations, but are merely the two aspects of the same 

 act of adjustment to environmental conditions. In some con- 

 nections it may do no harm to say that the wet situation causes 

 the long stem and causes the slime mould to climb up, but for 

 biological purposes all such statements must mean very little 

 until we know something of the chain of events between the 

 wetness and the building and climbing. Still less defensible is 

 the policy of saying that the stem is " caused" by the environ- 

 ment while the motion is "spontaneous" in the organism. 

 Mechanical biologists would be consistent, at least, in ascribing 

 both acts to " stimuli." 



The myxomycetes have long been objects of special interest in 



