Macbride: Ways of the Slime-Mould 



333 



of the more delicate species is more wonderful, more marvelous 

 still. 



The keen-eyed Swede, in what he could see with the lenses of a 

 hundred years ago, never ceased his expressions of wonder ; they 

 are on every page: According to his theory, vegetation is always 

 a matter of expansion, fruiting of contraction. And so when the 

 Plasmodium of some Trichia, Craterium or Arcyria, oozing up 

 from its hidden nutritive base, began to spread before him in hun- 

 dreds of thread-like streams covering the whole upper surface of 

 some forest-shaded log or some bed of smouldering leaves, he was 

 charmed ; sat watching hour by hour, until over the whole field the 

 threads began to break; rallying points not distant far from one 

 another appearing along each filmy line, he was delighted ; con- 

 traction succeeded expansion and he was satisfied. But when he 

 returned perhaps on the following day to find that from every 

 point a tiny stem had arisen, each surmounted by a glistening 

 spherule large enough, unless perfectly erect, to bear the little stem 

 to earth, his admiration knew no bounds ; he said, " I find nothing 

 more wonderful in all the world of plants." 



We of today, seeing so much better and knowing so much more 

 exactly the substance with which we have to deal, may, if we stop 

 to reflect, be no less surprised than was our old-time master. We, 

 far better than did he, know the nature of that thready stream, 

 and may be moved perhaps to greater wonder when it ascends and 

 stiffens several millimeters above the general level, and ends by 

 bearing a sphere upon the expanded summit. 



I am free to confess that I watched the procedure long before 

 I learned its methods. 



Any such mass of naked protoplasm as that we now discuss 

 shows to ordinary observation a differentiated ectosarc, in appear- 

 ance not very different from that which it incloses, but still dis- 

 tinct. This ectosarc, then, above occupies no doubt the field of 

 surface-tension. As the physicist has taught us surface- and mass- 

 tension are and remain in relative equilibrium as obedient to some 

 internal force, the currents of the plasmodium push their varied 

 way. But once in the physiologic history of the organism, the 

 tension equilibrium is at any point disturbed in favor of the mass, 



