On the Potato Disease. 71 



Another species Spicaria Solani, is thus described. 



Floccis albis, decumbentibus dense intertextis, ramulis fertili- 

 bus vulgo quatuor erectis, sporidiis minimis ovalibus concoloribus. 



Some of these species are only found in the internal cavities 

 caused by disease, others in cavities under the skin through which 

 they eventually pierce and then expand to a very considerable 

 comparative bulk. In one instance and one alone Prof. Harting 

 has perceived the formation of a particular fungus within the sac 

 of a perfect cell ; ordinarily their commencement is on the edges 

 of internal cavities among the remnants of destroyed cells. In 

 this instance the potatoes were of a particular variety from the 

 vicinity of Coblence. The fungus belonged to the genus Oidi- 

 nm, (Link,) or Oospora, (Wall worth,) and was named by Prof. H. 

 Oidium violaceum. Its characters are : 



Floccis ramosis violaceis, fertilibus in sporidia subglobosa sece- 

 dentibus. It is therefore quite different from any of the others. 

 Von Martius does not appear to have met with this, but he de- 

 scribes several other distinct varieties. Payen mentions one of 

 the same nature, but of an orange color. 



These fungi seem not to be capable of spreading by infection. 

 A large number of experiments were made upon this point ; some 

 of their sporules were placed in contact with freshly cut potatoes 

 and allowed to remain in contact under favorable circumstances 

 for many days ; in no case was a fungus of the same species re- 

 produced. This would appear to be conclusive, but von Martius 

 and Payen, both obtained results of a different character. In 

 any case we may conclude that it is not a very easy matter to 

 spread infection in this way. 



When the brown or black liquid matter, which appearing in 

 the sacs of the cells, is the first visible proof of disease, is placed 

 in contact with a freshly cut surface, the disease is readily com- 

 municated, but not if the skin of the tuber be perfectly sound 

 and unwounded. A very curious additional fact is, that in this 



pears 



Martius 



ascribed to insects. During the early stages of the disease noth- 

 m g is to be seen of them or their larvae. They usually appear 

 at about the same time as the fungi. Ordinarily two species are 

 observed, Glyciphagus fecularum and Tyrogliphus feculse. Later 

 m the disease, a species of Rhabditis sometimes appears of the 

 ^tne class as those which are found in vinegar, &c. These are 

 °% some of the more common varieties which occur. 



* rof. Harting has made a partial chemical investigation of the 

 difference between the sound and the diseased portions of the 

 tubers. The reaction of the sound portions was acid, that of the 

 juseased alkaline, with an evolution of ammonia. As might 



be 



supposed from this, the quantity 



s educed in the unsound portions, disappe 



