26 



MANUAL OF BOTANY 



Fig. 36. 



far as their roots are conoerDsd, entirely dependent upon the 

 plants on which they grow for their food. Others obtain their 

 food at first, like other plants, by means of the ordinary roots 

 contained in the soil ; but after having arrived at a certain age, 

 these perish, and they then derive their food entirely from 

 haustoria which penetrate the plants upon which they grow ; 

 others, again, continue throughout their life to derive a portion 

 of their food b}' means of roots imbedded in the soil, while they 

 possess in addition haustoria which are inserted into the roots of 

 plants growing side by side with them. These are often called 

 root-parasites ; besides taking in food from the soil and from 

 their host plants, they absorb nutritive material from the air by 

 their green leaves. 



It will thus be seen that parasites differ from other plants in 

 the fact that they are not entirely dependent for the raw 

 materials of their food upon the soil and from the air, but derive 

 at least some of it in an assimilable 

 state from the plants on which they 

 grow. Tlius, when green, Uke the 

 Mistletoe, they obtain a portion of their 

 food, like ordinary plants, from the air ; 

 but if of other colours than green, all 

 of it is derived by their roots from the 

 plants on which they live. It must 

 also necessarily happen that parasites, 

 by living partially or entirely upon 

 those plants on which they are placed, 

 frequently injure and even destroy 

 them, and in this way great damage 

 is done to Clover, Flax, and other crops 

 in this country and elsewhere. 



Besides the parasites just described, 

 there is also another class of plants 

 called sapro2]hytes, which, whilst 

 agreeing with parasites in deriving 

 their food from already formed organic 

 material, differ from this latter class in 

 growing on dead organic substances, and therefore assimilating 

 such matter as is in a state of decomposition or decay. Such 

 plants as Mviioiropa Hypoxiithys, Corallorhiza innata, Epipb- 

 giuvi Gmelini, and Heottia Nidus-avis, together with the greater 

 number of Fungi, are examples of Saprophytes. 



In the plants which are lower in the scale than the vascular 



l'i(f. 36. Lower part ol' tlic 

 ^tem and root o£ tlie com- 

 mon Stock, r, Tlie root 

 with its branches. /. The 

 stem. /, /. Leaves, h, b. 

 Leaf-buds. 



