606 GEOLOGY. 



pauperitic nature in the tissues and general aspect of the plant, while 

 the flowering was greatly restricted, and in some cases prevented alto- 

 gether. At the same time it was shown that, temporarily, the photo- 

 synthesis of the carbon dioxide was increased, and that the leaves 

 were engorged with starch. The inference was drawn that the dwarf- 

 ing effects were due to a disturbance in the adjustments of the plant, 

 This might perhaps be overcome in time by means of a gradual change, 

 so that no safe conclusions can be drawn relative to the effects of 

 a variation in the proportion of carbon dioxide brought about by a 

 change of geological slowness. It is to be noted, too, that the plants 

 experimented on were all angiosperms, and may be more subject to 

 disturbance by increased carbon dioxide than the lower groups which 

 lived in Carboniferous times. 



The seemingly conflicting import of the preceding considerations 

 lends uncertainty to all inferences, and invites reserve in interpreta- 

 tion, as well as more critical study in the field and laboratory. 



II. The Land Animals. 



The animal life of the land embraced amphibians, insects, spiders, 

 scorpions, and myriapods. The development of the amphibians was 

 the most significant feature, for it was the initiation of the great line 

 of land vertebrates, the ruling dynasty from that day to this. 



The rise of the amphibians. — Tracks attributed to amphibians 

 occur as early as the Devonian. In the Mississippian, there is a similar 

 record of a four-footed animal of thirteen-inch stride, believed to have 

 been made by one of the primitive amphibians, but in neither of these 

 periods have any relics of the animal itself been found in America, 

 and only imperfect fossils in Europe. These are sufficient, however, 

 to fairly attest the presence of land vertebrates. The amphibian 

 relics from the Carboniferous beds confirm their earlier presence by 

 such a degree of structural differentiation as to clearly imply a long 

 antecedent existence. The conditions of the Devonian period must 

 surety have been peculiarly favorable for the evolution of the amphib- 

 ians, for fish having structures akin to the amphibians, and appar- 

 ently susceptible of amphibian development abounded, and there 

 was much shifting of land and water areas, and doubtless much 

 competition and conflict and forcing of new adaptations, as a 



