30 



darkened bell-glasses and were carefully examined daily. In 

 nine months the oginia had doubled their size, and from being 

 smooth round bodies they changed into semi-transparent 

 brown rough bodies. The resting spores could then be seen 

 within the oginium or sac, and in some cases two resting 

 spores were within one sac. 



In the beginning of May a number of these burst and broke 

 into atoms, discharging a small bladder which also perished in 

 dust ; these were supposed to be effete spores. Others became 

 darker, and through their structure the formation of zoospores 

 could be distinctly observed. The zoospores were hyaline, 

 and were eventually expelled, but after laying quiescent for a 

 little time, two curved filaments appeared, they became straight, 

 quivered a little, and swam out of the field of view, similarly 

 to the zoospores from the acrospores on the fertile stem. 



The cilia or filaments eventually perishing, the zoospores 

 rested, they then threw out mycelium threads from which a 

 fertile stem with acrospores was propagated ; but the 

 conditions being unfavourable, the growth was abnormal. The 

 resting spores did not all produce zoospores, some of them 

 produced a long jointed thread only. 



The slides now under the microscope were made eight or 

 ten days ago from dried specimens brought from Lancashire, 

 England. The fertile stem, acrospores, mycelium, and resting 

 spores are distinctly visible in one of the slides ; the zoospores 

 may also be observed, but very minute and without cilia. The 

 filamentous white tuft of fertile stems is shown on another 

 slide as an opaque object under a two-thirds of an inch 

 objective. A glance at this object will enable the observer at 

 ■once to identify the fungus on the potato plant if perchance it 

 should appear in his kitchen garden ; it is a beautiful object ; 

 it has the appearance of a minute crystal forest ; the stems, 

 the branches, and the fruit, all transparent and glittering ; its 

 beauty is however but short-lived, for when it touches it 

 destroys, and as its victim falls its own beauty passes away, its 

 power" to destroy still remaining. 



The P. infestans is nearly always in company with the 

 Fusisporiwn solani, and it requires not a little practice to 

 distinguish between the two kinds of spores. The Fusisporium 

 spores are much smaller, 1/2500" in diameter, and finely 

 muriculated. They are equally destructive. 



The P. infestans seem to vegetate most luxuriantly on 

 plants that are grown on undrained ground, or on ground that 

 has been dressed with rich hot manure ; the plant, being 

 saturated with moisture and forced with the manure, is 

 delicate and appears unable to resist the attack, especially in 

 warm rainy weather. 



The crops on sandy soils appear to suffer the least from this 



