426 Minnesota Plant Life. 



So, too, if a thermometer l)iilh is imbedded in a l)unch of violets 

 and laid in the sun, while another is imbedded in a bunch of 

 primroses, the one in the violets will re,£^ister a higher tcm])er- 

 ature after both have been lying tog-ether in the sunlight. The 

 recognition of the warming-up color of plants as a heat-pro- 

 ducing substance gives a basis for the explanation of a great 

 many facts that would otherwise l)e difficult to understand. 

 Autunui foliage can be imderstood to be a definite response of 

 the plant to the falling average temperature, by the development 

 of a heat-producing area of its own. The purple bud scales, so 

 common in trees that grow outside the tropics, ])urp]e tints 

 in bark and in leaves, and the purplish or reddish colors of 

 flowers, are all recognized as having the same general signifi- 

 cance. 



At this point it is possible to understand how, in a great many 

 species, the color of flowers may have originated. As has already 

 been explained, the flower is essentially the end of a branch, and 

 the coloring substances which it contains are possibly to be 

 attributed to protective heat-producing substances present in 

 the race-history long before flowers were developed as such. 

 When flowers came to be formed it was important that their 

 pollen should be protected against cold, and the heat-i^roducing 

 colors were not abandoned but accentuated. In many blue, 

 violet and red flowers it is possil)le to read a story of defence 

 against cold. Hence is made clear the reason for so many 

 very earlv flowers, like the pascpie flower, maple flowers, violets 

 and anemones, being puri)lish in color, and for late flowers, 

 such as the gentians, having the same blue or purple hue. It 

 is also easy to understand how flowers on the mount:.iin tops 

 should be so often blue and that flowers of the polar regions 

 should show the blue, violet or reddish tints. With such facts 

 in mind it is possible to recognize violets and anemones as, for 

 the most part, northern ])lanls, while goldenrods and e\ening- 

 prinu'oses indicate a southern origin. 



Another useful habit of plants in polar regions is their tend- 

 ency to form stores of reserved food-material, such as under- 

 ground fleshy roots, stems or tubers, or subterranean bulbs. .\ 

 great variety of plants with such habits are eoinnmn in Minne- 

 sota. On account ol il> pro\i(leni beha\i(,)ur the i)lanl is able 



