8 DISEASES OF FIELD & GARDEN CROPS. [en. 



Theocritus) to pierce, pin, or transfix, or perone, the pin 

 or tongue of a buckle, a pointed or piercing object, and 

 spora (<nropa), a seed or spore. He probably used the 

 word in reference to the power of the fungus to pierce the 

 tissues of the plant it attacks as distinguished from other 

 fungi which have no such power. The specific name 

 trifoliorum explains itself. Peronospora trifoliorum, D.By., 

 is closely allied to the potato fungus, and it grows within 

 and upon the under surface of the leaves of the plants in- 

 vaded. By this habit of growth, and its putrefactive power, 

 it not only chokes up the organs of transpiration of the host 

 plant, but causes decomposition of the tissues by contact. 

 It is remarkable for the profuse production of its minute, 

 oval, transparent spores or conidia. A spore in fungi is a 

 reproductive body, answering to the seed of flowering 

 plants, but with no embryo or rudimentary plant within. 

 Certain spores in Peronospora and in many other fungi are 

 often called conidia from fcom'a, dust, to distinguish them as 

 secondary spores, or spores of an inferior class, the fungus 

 itself being capable, under favourable circumstances, of 

 producing other spores of a much higher order and more 

 complex structure. The conidia in Peronospora, as the 

 name indicates, are like fine, generally transparent dust. 

 These conidia are filled with colourless protoplasm, or vital 

 material, and they do not readily germinate except in 

 water. When a conidium of Peronospora trifoliorum, 

 D.By., falls upon any damp surface it bursts at the side, 

 and the protoplasm exudes somewhat in the form of an 

 amoeba, one of the simplest animal organisms. From this 

 irregular amoeba-like form, other fertile stems of Perono- 

 spora trifoliorum, D.By., speedily arise. 



The disease spots on the leaves, as caused by the Perono- 

 spora, are at first white, and speedily become pallid or 

 brownish. At length the corroded fragments drop from 

 the leaf to the ground. This species of Peronospora pro- 

 duces oospores, egg -like spores or resting - spores ; these 

 fall to the ground in the autumn, and rest in a hibernat- 



