CLIMATIC. 81 



We must also consider that the water evaporated does not all escape into 

 the air as vapor, but a goodlj percentage is reabsorbed by the leaves as 

 soon as breathed out and fitted in the sunned air for wood growth again. 

 To a great extent plants adapt themselves to the amount of water at their 

 disposal. 



TRANSPIRATION. 



By transpiration is meant the water consumed in building up the body 

 of the plant; the larger part being returned to the atmosphere during the 

 process of growth. In this operation the quantity of water used is as 

 variable as the quantity of precipitation. "Many considerations enter into 

 the operation the stage of plant development, nature of its leaves and 

 amount of its foliage, temperature and humidity of the air, intensity of the- 

 sunlight, temperature and structure of the soil, etc." 



EFFECTS OF OUR NORTHERN FORESTS UPON VEGETATION. 



Note the following facts adverted to by Prof. L. A. Bailey, Jr., of the 

 Agricultural College of Michigan, who, with Professors Warren Upham, 

 E. W. D. Holway and others, assisted our state geologist, Prof. Winchell, 

 in the botanical work of Minnesota in 1886. The expedition, commencing 

 July 17th, was located at the south end of Vermillion Lake, near Tower, at 

 about 48 degrees north latitude, whence they radiated in all directions, 

 mainly between that point and the international boundary. Though their 

 search was systematic, they found "a discouraging paucity of species." 

 Their discoveries were "an illustration of the law, that species decrease 

 with the increase of latitude," and correspondingly, that "the ligneous 

 vegetation simply makes a smaller growth." Summing up the situation, 

 Prof. Bailey says: 



"In some respects the flora of this region is anomalous. In most of its 

 features it differs little from that of Central Michigan, six degrees to the 

 southward. This southern cast to the flora finds a ready explanation, 

 however, in the fact that Vermillion Lake is separated from the cooling 

 influences of Lake Superior by a degree of primeval forest. It is probably 

 not so much the character of the winters as that of the summers which 

 influences th3 distribution of plants in these latitudes. The snow must 

 afford great protection to all vegetation at this place, and the summers, 

 although short, are warm and the atmosphere is dry." 



TREES CREATE CONDITIONS. 



No doubt "the one degree of primeval forest" has something, perhaps 

 much to do in mitigating the severity of the cold winds from Lake 

 Superior. But there is a greater factor involved than a strip of seventy 

 miles of trees. In determining the features of flora in any part of the 

 country, we should first take into our account the prevailing air currents 

 and isothermal lines which woodlands more or less direct and modify. 

 Writing the editor in this connection, H. B. Ayres aptly says: "The 

 herbaceous flora of Minnesota should be expected to be similar to that of 

 Michigan, because the forests create conditions needed by certain plants. 



