HOW PLANTS OBTAIN FOOD. 



87 



of these plants which are known as parasitic fungi. The plant at whose 

 expense they grow is called the "host." 



One of these parasitic fungi, which it is quite easy to obtain in green- 

 houses or conservatories during the autumn and winter, is the carnation 

 rust (Uromyces caryophyllinus), since it breaks out in rusty dark brown 

 patches on the leaves and stems of the carnation (see fig. 75). If we make 

 thin cross sections through one of these spots on a leaf, and place them for a 



Fig. 76. 

 Several teleutospores, showing the variations in form. 



few minutes in a solution of chloral hydrate, portions of the tissues of the 

 leaf will be dissolved. After a few minutes we wash the sections in water on 

 a glass slip, and stain them with a solution of eosin. If the sections were care- 



Fig. 77. 



Cells from the stem of a rusted carnation, showing the intercellular mycelium and haustoria. 

 Object magnified 30 times more than the scale. 



fully made, and thin, the threads of the mycelium will be seen coursing be- 

 tween the cells of the leaf as slender threads. Here and there will be seen 

 short branches of these threads which penetrate the cell wall of the host and 

 project into the interior of the cell in the form of an irregular knob. Such 

 a branch is a haustorium. By means of this haustorium, which is here 



