FUNGOID PESTS OF CULTIVATED PLANTS. 91 



That on Celery occurs also in Germany, Austria, Italy, and the United 

 States. 



Sacc. Syll. iv. 2125 ; Tubeuf, Dis. 514 ; Sacc. Fl. Ital t. 667. 



LETTUCE ROT MOULD. 

 Bremia Lactuca (Regel.), PL IX. fig. 115. 



The mould which causes this disease appears to have been known 

 since 1843, but it was in 1846 that Berkeley first drew attention to the 

 pest, and considered the mould to be the cause of the rot. Afterwards it 

 came to be known under the name of Peronospora gangliformis which 

 has since been abandoned in favour of the above name. 



There is an abundant mycelium present in the leaves before the mould 

 appears on the surface. This is thick and coarse, being furnished with a 

 number of club-shaped suckers or haustoria. From the mycelium arise 

 the erect fertile threads through the natural orifices of the leaves. These 

 are flattened, and from two to six times forked, without cross partitions. The 

 tips of the final branchlets are swollen in a peculiar manner, supposed to 

 resemble "ganglia." These swellings are somewhat of a saucer-shape, 

 with a single spicule in the centre and three or four more growing around 

 the edge. Each spicule bears a nearly globose spore, with a very minute 

 teat or papilla at the apex (16-22 x 16-20 /<) 



The resting spores are produced in clusters, and are plentiful in old 

 and decayed stems. They are nearly globose, not quite even, arid of a 

 tawny colour, exceeding in size the largest dimensions of the conidia 

 (28-34 p). 



Found chiefly throughout Europe and in the United States. 



For Lettuce rotting in greenhouses see Journ. E.H.S. xxvi. 1901, 

 p. 558. 



Sacc. Syll. vii. 243 ; Cooke, M. F. t. 14, f. 265 ; Tubeuf, Dis. p. 131 ; 

 Smith, Field Crops, 289 ; Mass. PL Dis. 74 ; Mass. B. F. 115, figs. 64, 

 65 ; Cooke, Hdbk. 1777. 



Lettuce leaf-spots are known abroad, and anthracnose in the United 

 States. 



POTATO SPINDLE MOULD. 

 Fusarium Solani (Mart.), PI. VIII. fig. 116. 



Because this parasite was so commonly found upon Potatos in decay 

 it was for a long time supposed that it was only a companion of the 

 Potato murrain, or a consequence of decay. Latterly it has been closely 

 watched, with the conclusion that it is really a destructive fungus on its 

 own account, and will attack stored Potatos, whether bruised or not. 



It grows either in company with the rot mould or also independently 

 upon tubers which exhibit no trace of decay. The mycelium is similar 

 in both, but the resulting moulds are different. The fruiting threads of 

 the Fusarium or "spindle mould" are shorter, and for the most part 

 unbranched, bearing at their tips the fusiform or spindle-shaped spores 

 or conidia, which are a little curved, and set rather obliquely upon 

 the threads (40-60 x 7-8 /*). Each sporule is divided by transverse 



