276 INTRODUCTION TO CRYPTOGAMIC BOTANY. 



being the case. A species was found by Dr. Thomson in Tibet 

 on ZygophylluTn, and another in New Zealand on Aristotelia. 

 Dry weather and warmth, to a certain degree, seem to be 

 favourable to their growth, as is notorious in the hop and 

 turnip mildew ; but they do not seem capable of enduring a 

 great amount of heat. The encaustic mycelium of Meliola 

 (Fig. 62, d, e), which grows generally on the firmer leaves, sup- 

 plies their place in the tropics and subtropics, causing scarcely 

 less damage, where it is prevalent. The sporangia are far larger 

 in this genus, but, like the last, are surrounded by processes 

 springing immediately from their walls. While in Erysiphe 

 the sporidia are small, in this they are peculiarly large. With 

 it are associated in the work of destruction, species of Anten- 

 naria, which are, probably, only the mucedinous state of 

 Capnodium, (Fig. 63, a, b, c), a genus which is common to warm 

 and temperate parts of either hemisphere. In that genus the 

 perithecia, which are evidently formed or at least incrusted by 

 processes of the mycelium, sometimes yield distiact asci and 

 sporidia ; while in other cases they are only pycnidia, and 

 produce naked spores. In Antennaria, the sporangioid bodies 

 sometimes contain a ready-formed miniature plant, which 

 waits only circumstances favourable to its expansion. It is 

 curious that, as in Erysiphe the pycnidia appear frequently 

 to arise from the transformation of one of the joints of the 

 moniliform threads (Fig. 20, a), so the fruit of the Antennaria 

 stage of Capnodium is a more perfect organization of indi- 

 vidual articulations. In both cases the walls, which were 

 originally uniform, become cellular. Lasiohotrys differs from 

 allied genera in its subcuticular growth. Scorias is an exag- 

 gerated form of Capnodium, and is gelatinous and very 

 thick when moist. At present it has been found only in the 

 United States. 



281. The black mildews have of late years raged to such an 

 extent in the Azores and Ceylon as to threaten the complete 

 annihilation of the orange and coffee plantations, and the 

 ravages have been scarcely less amongst the oUves in some 

 parts of Europe. It is impossible that light can have its 

 proper effect through such a medium on the tissues of the 



