Page:Popular Science Monthly Volume 18.djvu/817

Rh . The use of the stick or stone in defense set in motion a new process of adaptation which has tended toward a physical weakness, at least in regard to conflict with wild animals.

It was, in fact, the first step in the enhancement of animal force by the employment of the vast stores of inorganic force existing throughout nature. It was the earliest inventive action, the bringing of outer nature to human aid, which has since produced such wonderful results. Muscular vigor and acuteness of sense have probably decreased as they have been thus partly replaced. For man has gained new muscles, in his use of the forms and forces of the inorganic world, and has commenced a new process of adaptation, which has already enabled him to extend his kingdom from the tropic to the frigid zone, and which promises to make him to some extent master of the fields of water and air. And his mental experience of wider and wider conditions of nature has produced a new form of physical adaptation—that signified in clothing and habitation.

But this opens a new subject, too wide to be considered here. We can only end as we began, with the assertion that the human form occupies the apex of possible organic development, and forms the true foundation for that higher mental evolution which is still growing, branching, and flowering upward.

 

HE isothermal line, curving up and down the map, is no inapt illustration of the course another line would take on the chart which sought to explain the relative hardiness of plants, only the curves of the latter would be more complex than those of the former. Who, indeed, could direct aright such a line for even individual species? and for varieties it would be wellnigh impossible. Scarcely could reliable data be furnished for the broader division of genera. And yet the investigation that does not take into account varieties misses a large number of plants possessed of the most noteworthy and valuable individual traits. The question may be easily asked, Wherein lies the difference between a variety and a species? but the answer evidently is not so easy, when we consider that every individual plant varies in a degree from all other plants; and, to render it still more difficult, we find botanists very properly ignoring the existence of varieties that may have individual characteristics invaluable to the planter.

Latitude, moreover, we find is only one factor, and a very vague one, in the problem of determining the relative hardiness of plants. Climate is the real governing. element—climate, that varies with the 