306 



THE DISEASES OF PLANTS. 



are three species of Cuscuta, one of which attaches itself 

 exclusively to the vine : its filaments are as large as a 

 small packthread ; fortunately, this last is very rare. 



The Orobanche is a genus, one species of which adheres 

 to the roots of hemp, and destroys them by devouring 

 their juices. 



Fungi form a very considerable class of false parasitical 

 plants ; to this class belongs the Erisiphe, which attacks 

 the leaves of plants: it first makes its appearance under the 

 form of yellow spots, which afterwards turn black. There 

 are no less than forty different species of this parasite. 



The Rhizoctonia is a species of fungus, which confines 

 itself almost wholly to the roots of lucerne and saffron : 

 this disease manifests itself by the fading of the head of 

 the plant, and the contagion soon spreads around it, in 

 rays as from a centre. If one of the affected plants be 

 pulled up, the roots will be found covered with the nox- 

 ious filaments of this fungus : their effects on saffron is so 

 baneful, that the malady it produces bears the name of 

 death; and the only way to prevent its spreading, is to 

 bury the affected plants in a sort of cemetery, for it is ne- 

 cessary to surround them by a ditch ; and in digging it, 

 care must be taken to throw the earth inwards, to prevent 

 the contagion from spreading. There are three species 

 of this destructive fungus, the brown, the carmine, and the 

 white : the latter attacks fruit trees ; its filaments are free 

 from tubercles, while those of the former are covered with 

 them. 



The class of internal fungi is very numerous, there be- 

 ing not less than three hundred species, each attaching 

 itself to the plant which suits it. Some of them attack all 

 the plants of the same family ; others confine themselves 

 to those of the same species. Two of those species of fungi 

 belong to the rose-tree : they appear at first under the form 

 of small yellow spots; these increase till they run into each 

 other ; their color then changes to various tints of brown 

 and red, tints which you must have observed the leaves of 

 the rose-tree often assume, long before their natural decay. 



1650. What are the three species of it 1 ? 1651. What is said of the 

 Orobanche'? 1652. What is said of the Erisiphe'? 1653. And of 

 the Rhizoctonial If one of the plants affected by it be pulled up, how will 

 the rools appear 1 1654. What are the three species of this fun- 

 gus 1 ? 1655. What is said of the class of internal fungi? 1656,^ 

 And of the two species which belong to the rose tree! 



