422 Minnesota Plant Life. 



gale along the lee shore of some Minnesota lake, one may see 

 the bulrush stems beaten into the water by the wind and surf, 

 only to rise again erect and unharmed when the waves are 

 calm. Such elasticity is procured by special structural areas 

 in the stem, disposed in highly accurate fashion so as to take 

 up the lateral strains evenly and effectively. The cross-section 

 of a bulrush stem shows it to be as cunningly constructed as the 

 finest bridge-truss, with girders, flanged in the regulation style, 

 made up of the so-called "tension pieces" and "compression 

 pieces" of the architect, and constituting an altogether admi- 

 rable piece of structural engineering. Such contrivances are 

 not needed by plants growing under other conditions and will 

 not be found. Elasticity, for example, is not a noteworthy char- 

 acteristic of the stem of submerged aquatic plants living in 

 quiet pools ; but if the stem grows in running water it is some- 

 times more elastic. Roots, in general, being underground in 

 their habit, are not so much exposed to occasional displacing 

 forces as are stems and, therefore, are by no means so elastic. 

 It is easy to compare, in these regards, a grass stem and a grass 

 root. If the living erect stem of a rye plant is bent down it 

 quickly resumes its original position ; but if the root is bent to 

 one side the resumption is but slight, or there is no resilience. 



In certain parts of the world, where heavy falls of snow occur, 

 a weight is in this way piled upon the branch system, and the 

 plant perhaps responds to such a climatic state by growing in 

 the form of a flat, prostrate shrub, as many of the heaths have 

 done. Or, if it be a tree, it learns to produce strong drooping 

 lateral branches like those of the spruces. When grown in a 

 lawn, these trees retain the droop of their branches or branch- 

 lets originally a structural device for shedding masses of snow, 

 that might otherwise break the branches by their weight. 



Plants that produce abundant and heavy fruits must, if they 

 support the weight of these fruits, develop strong branch sys- 

 tems, or otherwise the body of the plant will be broken. Of 

 this the apple trees of orchards furnish good examples. The 

 branches of the apple are pulled into a more horizontal posi- 

 tion by the increasing weight of the fruit and many of them 

 actually droop. The main branches will, however, be found to 

 be strong and well buttressed against the trunk. Very often, 



