438 Minnesota Plant Life. 



clays, less copiously branched root systems are produced. The 

 temperature of the soil, as well as its texture, has a variety of 

 well-marked effects upon root areas, as has also the consist- 

 ency, the chemical constitution and the aeration. Soils which 

 are very poorly aerated, such as those disposed underneath 

 sheets of water, often make it necessary for roots developed in 

 them to send up aerating tubes or organs. The well known 

 "knees" of the swamp cypresses of the Atlantic region are ex- 

 amples of such organs. A greater or less percentage of nitrog- 

 enous substance, lime, magnesium, iron or silica, in the soil 

 has a distinct determining effect upon the forms of plants. 



Especially interesting is the soil known as humus, a type 

 which contains a large percentage of decaying organic material. 

 In such a soil many plants without leaf-green are enabled to 

 grow, and upon the humus of the forest floor a wealth of mush- 

 rooms, club-fungi, cup-fungi, slime-moulds and various related 

 forms are displayed. Some seed-producing plants, such as the 

 pine-drops, the Indian-pipe, and the pine-sap, together with the 

 coralroots and others, have learned to abandon their leaf-green 

 and have adopted the habits of life similar to those of the fungi. 



Other living things. The proximity of other living things 

 is a condition of the surroundings that cannot be disregarded in 

 the discussion of plant adaptations. These neighboring crea- 

 tures may be either plants or animals. In response to their 

 presence a large variety of curious structures and habits have 

 come into existence. The carnivorous plants catch and eat 

 small insects with which they come in contact. Parasitic fungi, 

 such as the caterpillar fungus or the fly-cholera fungus, attack 

 certain small animals and use their bodies for a soil in which 

 to grow and mature. The roots of louseworts, toad-flaxes, and 

 cancerroots, reach out and attach themselves to the roots of 

 neighboring plants, in some instances deriving their whole 

 sustenance in this manner. A great variety of little fungi 

 develop upon the leaves, twigs, flowers or fruits of other plants, 

 having become accustomed to eke out an existence in this 

 dependent manner. Many plants perch upon other plants; 

 thus, the Spanish moss of the south hangs in festoons from the 

 live-oaks, and the orchids of South America sit in rows, like so 

 many partridges, upon the branches in the forest. The lichens 



