168 THE AMERICAN MONTHLY [June, 



with strong thread ; immerse in 95 per cent, alcohol for ten min- 

 utes, then separate slides and transfer section to oil of cajeput ; let 

 it remain in the oil for two or three days, then mount in balsam. 

 By this method the trichinae will not "disappear" as they some- 

 times do by other methods, nor will they shrink. 



Fig. No. I is stained with picro-carmine, and is a most beauti- 

 ful mount. The photomicrograph from which the illustration 

 is made was taken by ordinary lamp-light and Carbutt's ortho- 

 chromatic plate. The other preparations, as illustrated, are by 

 the same method from unstained sections. 



The writer would be glad to exchange "photos" of Fig. i for 

 pieces of fresh or hardened trichinous meat. 



The American Potato Rot or Blight. 



By JOSEPH F. JAMES, 



U. S. DEPARTMENT OF AGRICULTURE, WASHINGTON, D. C. 



The potato plant has probably been subject to the attacks of 

 fungi as long as it has existed. Under the bark of trees living 

 during the time our coal was forming, there have been found fos- 

 sils so similar to living examples of potato fungi, as to induce the 

 belief that they were the ancestors of modern species. 



It is a well-known fact that when a plant is removed from its na- 

 tive habitat and subjected to a diversity of conditions, and more 

 especially when extensively cultivated, there appear upon it para- 

 sites, before unnoticed, that with increased cultivation multiply 

 and spread with wonderful rapidity. So well known is this that 

 it has sometimes been suggested that in order to develop a pest to 

 destroy a pernicious plant it would be wise to cultivate the plant, 

 and before long it would be attacked by numerous enemies, and 

 its numbers thus lessened. It is scarcely probable that any actu- 

 ally new species of insect or plant enemies are developed in the 

 process of cultivation, but having a more extended field in which to 

 work they multiply in undue proportion, so that they kill the host 

 upon which they feed. Thus it has happened that, although the 

 potato was introduced from the New World into Europe shortly 

 after the discovery of America, the destructive disease of the tuber 

 did not attract any great attention until about 1830. Some sort 

 of disease was noticed some ten or fifteen years before, but it was 

 not until iS44that tlie matter was inquired into by scientific men. 



In 1S46 it was shown conclusively by Berkeley that the disease 

 was caused by a fungus, now well known as Phytophthora {Pe- 

 ronospora) i?tfestatis. Since then exhaustive studies have been 

 made of the parasite, and now, not only is its life-history well- 

 known, but means for its prevention have been discovered. 



The disease commonly spoken of as potato blight, in this coun- 

 try, is caused by two distinct species of fungi. One of these is the 

 Phytophtho7-a, already referred to, and which is the blight of 



