150 



TUBNIP AND CABBAGE-ROOT ATTACKS. 



extent microscopically ; but not being a regular fungologist, I give the 

 following abstract of the main points of life-history of this Slime Fun- 

 gus from the digests of Prof. Marshall Ward and Mr. Worthington 

 G. Smith.* 



It appears that if a section of a diseased root is examined micro- 

 scopically, a portion of the greatly enlarged cells will be found filled 

 with what may be called spores, or spherules, or (generally) a formation 

 from which a young " Slime Fungus " will presently emerge. These 

 are stated to be packed so closely in the containing, much enlarged, 

 plant cells, that (to use the words of Prof. Marshall Ward) these " look 

 like bags of small shot," but they need strong microscopic powers to 

 distinguish them clearly, each spore being only about one six-hundredth 

 part of a millimetre in diameter, that is, about one six-hundredth part 

 of a twenty-fifth part of an inch. 



Spores and embryos of " Slime Fungus," Plasmodioplwra brassic<e, after Woronin. 

 Nat. size of spores about one six-hundredth of a twenty-fifth part of an inch. 



Each of these minute colourless spores, or spherules, is composed 

 of a little speck of what is called "protoplasm " (or formative material) 

 surrounded by a cell wall of delicate membrane, as figured at "1." In 

 this condition the spores are stated to pass the winter m the rotten 

 roots, or in the earth where they may have been dispersed by the 

 decaying of the roots in which they were formed. After the " rest " 

 season has passed the spore splits on one side, and the contents 

 gradually make their way out, as figured at " 2 " and " 3 " ; and at 

 "4" the irregularly shaped growing mass is shown as completely 

 escaped. These masses soon become furnished with a long tail-like 

 process " 5," and with the help of these tails, hairs, or cilia, these 



* A plain and serviceable account of the life-history of the Plasmodiophora 

 brassicce, with some good suggestions as to prevention of recurrence of attack, will 

 be found in ' Diseases of Field and Garden crops,' by Worthington G. Smith (Mac- 

 millan & Co.) ; and in ' Diseases of Plants,' by Prof. Marshall Ward (a small volume 

 published by the Society for Promoting Christian Knowledge), at pp. 47 — 58, a more 

 especially technical account is given of the history and action of the infestation. 

 For general information these two works are perhaps more serviceable than very 

 elaborate treatises. 



