Dependent Plants 73 



is abundant in the air. Nitrogen is a valuable and expensive 

 food material, and can be obtained by most plants only from 

 compounds in the soil. Legumes can not only obtain it for 

 themselves, by the help of these little bodies, but they leave 

 nitrogen compounds in the soil, to be used by other plants. 

 Just think of all the plants in this country which have pods 

 and belong to the pea family ! How they are enriching the 

 soil ! Yellowwoods {Podocarpus) have little plants living in 

 their roots which perform the same service. 



Plants which live together in this way and are helpful to 

 each other are called Symbionts. Plants are sometimes 

 symbiotic with animals. There is a kind of Acacia with little 

 holes in the base of the large hollow thorns. Within these 

 thorns ants make their nests. Other insects eat and injure the 

 leaves of the Acacia. The leaves manufacture a nectar which 

 is poured out at the very tips of the leaflets. The ants sally 

 forth in quest of the sweets, but on the way they make the first 

 course of their feast off the marauding leaf-eating insects. 



It has been suggested by the eminent German botanist, 

 A. Kerner, that the leafy members of the Mistletoe family are 

 symbionts with their hosts, making food in winter and giving it 

 up to the host when the leaves have fallen, and it cannot make 

 food for itself. 



Insect-eating Plants. — The Sundew (Drosera) obtains 

 its nitrogen from insects which the plant catches and digests 

 by means of the sticky tentacles which are 

 borne on their leaves and stems. Rori- 

 dula^ a small shrub belonging to the same 

 family, has the same habit. Dr. Marloth 

 has found that two animals live symbioti- 

 cally with Rorldula. The plant catches „ ^ t,, jj r 



-' _ ^ r IG. jo.—s, Bladder from 



flies for a spider which is saved the trouble a leaf o^ utriadaria 



c'ulgaris (X 4.) (From 

 of making a web, while the spider acts Thome' and Bennett's 



- " Structural and Phy- 



as a scavenger, removing the remains 01 sioiogicai Botany.") 

 the flies from the leaves. Strangely enough, 

 the spider can run where the flies would fear to tread if they 

 but knew the doom awaiting them. Another still smaller 

 insect lives within the flower and pays for its food by setting 



