114 DISEASE OF TURNIPS. 



to one of the most minute veinlets) which go to sti'engthen the 

 leaf. At the top and bottom of the leaf is a cushion of jointed 

 spawn or mycelium, closely interwoven ; and from these jointed 

 threads arise numerous jointed cluh-like branches. Each branch 

 is terminated by an elongated barrel-shaped spore, densely 

 filled with protoplasm and furnished with a cell-wall. In the 

 Bradford Abbas specimens these spores measure -00125 of an inch 

 in length, and this agrees well with the size orginally given by 

 Mr. Berkeley in the Gardeners' Chronicle, viz., from -0012" to 

 •0013". When Mr. Berkeley published this plant in the Annals 

 of Natural Kktory, he changed the dimensions to -0015", and 

 this is repeated in Dr. Cooke's Handhoolc. A glance at the illustra- 

 tion will show the number of spores that are visible on the 576th 

 part of a square inch as seen edgeways ; 8 or 10 times as many 

 would be really present on the cubical piece of leaf-blade here 

 illustrated. How many spores, then, must there be on one leaf, 

 on all the plants of one field, or dispersed over the hundreds of 

 acres near Sherborne ? How, too, can the plants grow with 

 such a cushion of spawn enveloping the foliage all over ? 



The spores germinate very readily ; they have only to be 

 dusted on to an uninfected leaf or on to a piece of clean glass, 

 and kept under a bell-glass in moist air. An opening speedily 

 appears at the edge of one of the ends of the barrel-like spores, 

 and through this opening a thread of spawn emerges, which 

 rapidly reproduces the parent Oidium. A germinating spore is 

 shown in fig. 74, f. a new inmature club is seen at g. The spore 

 is on a piece of Turnip-leaf, one of the stomata, or mouths, being 

 visible at c. 



The above is only a short part of the life history of Oidium 

 Balsamii : whence it comes, where it goes, what other form it 

 takes, on what plant it may then live, and how it hibernates, no 

 one at present knows. — From the Gardeners' Chronicle for Septem- 

 ber 25th, 1880. 



