4i 8 Minnesota Plant Life, 



the unrelated spurge family at the Cape of Good Hope. The 

 pitcher-plant and sundew have developed apparatus for catch- 

 ing small insects and converting them into food for their own 

 uses, and somewhat similar contrivances are met with in the 

 bladdcrworts and butterworts ; but the two groups of plants, so 

 far as true relationship goes, are very widely separated. With 

 such facts in mind, it is apparent that, if genealogical connection 

 be ignored, plants may be grouped according to their adapta- 

 tions. By this means certain interesting truths may be em- 

 phasized concerning the influence, upon plant structures and 

 habits, of the surroundings. Before entering upon any discus- 

 sion of the various adaptational groups of plants represented in 

 Minnesota, such as water plants, desert plants, carnivorous 

 plants, perching plants, mat plants, wand plants, shade plants, 

 sun plants, rock plants, marsh plants and a number of others, it 

 may be briefly noted what are the principal external conditions 

 to which plant structure and habits are adapted. 



Gravity. A plant, like any other natural object, must main- 

 tain itself under the constant influence of the force of gravity, 

 and it is, therefore, necessary that it should be architecturally 

 well constructed. An imperfectly constructed tree trunk could 

 not bear the weight of its branch-system, nor of its thousands 

 of leaves and possibly of fruits, unless precisely as in works of 

 man, such as elevators, aqueducts or bridges the laws of en- 

 gineering had been obeyed. Certain necessary ratios exist, 

 therefore, between the thickness of tree trunks, the tenacity of 

 the wood, the height of the tree, the number of branches, and 

 the angles at which they stand upon the main axis. For this 

 reason a limit is fixed for the height of land vegetation, beyond 

 which it is extremely difficult to pass. If, however, in the life 

 of the plant some method is found by which support can be 

 obtained from without, much longer stems can then be produced 

 and they can remain of slenderer habit. Thus the climbing 

 bittersweet, the wild grape vine, the trumpet-creeper, the pipe- 

 vine, or the bean, are enabled to produce stems much longer in 

 proportion to their thickness and strength than would be pos- 

 sible if they did not utilize neighboring vegetation to help bear 

 the weight of their leaves, twigs, flowers and fruits. The sup- 

 port that is obtained by a plant stem need not necessarily con- 



