28 DISEASES OF FIELD & GARDEN CROPS. [CH. 



ferentiation of the protoplasmic contents of the ascus. 

 Mixed with the asci are numerous slender, often septate 

 organisms, termed paraphyses (as at A, Fig. 9), or organs 

 which grow about or in company with organs of greater 

 importance. The word is derived from para, about, and 

 phud, I grow. The right hand ascus in the illustration is 

 shown in the act of discharging its sporidia into the air. 

 At a given moment, depending upon unknown conditions, 

 possibly of the air, of light or heat, the ascus opens at the 

 top, as illustrated (in some fungi an operculum or lid flies 

 off), and discharges the eight sporidia which it invariably 

 contains into the air. In the genus of fungi named 

 Ascobolus, the ascus itself, with its contained spores, as 

 the name indicates, is shot into the air. Each transparent 

 sporidium is furnished with two or three lustrous spots. 

 The asci are so inconceivably small, slender, and attenu- 

 ated that there are more than 300,000 packed side by 

 side on the top of each expanded cap, which on the 

 average measures about half-an-inch in diameter ; and as 

 each ascus contains eight sporidia there are no less than 

 2,500,000 sporidia produced by every cap. Now, as 

 every infected potato plant will produce at least fifty 

 Sclerotia, it follows that a plant killed by this new disease 

 is capable, by means of its germinating Sclerotia during 

 the following season, of discharging more than 100,000,000 

 reproductive bodies into the air. It must now be specially 

 noted that after a year's rest the Sclerotia germinate on 

 the ground, and there produce their sporidia exactly at 

 the time in July when potatoes are making their best 

 growth. A vast number of the sporidia must perish, but 

 such as fall upon potato plants (and possibly some other 

 plants, as carrots) germinate at once, cover the stems with 

 spawn, obliterate the organs of transpiration, and speedily 

 reduce the haulm either to a mass of putrescence or to 

 dry tinder. During this rapid and exhaustive growth the 

 spawn again gradually compacts itself into the black 

 nodules of condensed mycelium termed Sclerotia, and 



