FUNGOUS ROOT-TUBERCLES. 67 



formation of these tubercles is not confined 



definite 



3 various fixing solutions used, Kaiser's sublimate- 

 d iridium chloride gave the best results. After fixa- 

 material was hardened and imbedded in the usual 

 and transverse and longitudinal sections 5-8 in 

 thickness were made. For staining, Fleming's triple and 

 Heidenhain's iron haematoxylin stains were used, the triple 

 stain proving the better for differentiating the various host 



manner 



m 



determined 



haematoxyl 



prepared 



mycelium 



means for the studv of the minute 



and the host, although examinations of fresh material were 

 made in an attempt to obtain pure cultures, and the testing 

 of the enzymes present in the tubercles of course was done 

 with living material. The result of this work is deferred to a 

 subsequent paragraph. 



External Characters. 



All the plants of Ceartothus americanus examined pos- 

 sessed tubercles on their roots; the youngest plants have 

 only a few, often not more than two or three, whereas older 

 plants have a large number; one nine years old possessing 

 1,830 tubercles on the roots. The number thus increases with 

 the age of the plant and with the root mass, a fact contrary 

 to conditions found in the alder, where very old trees do not 

 seem to have as many as the younger and more rapid grow- 

 ing ones. The tubercles are also found at a greater depth 

 than with the alder, the greatest number and the largest 

 coral-like clusters being usually found 4-10 inches below the 

 surface of the soil. When there are but a few lateral roots 

 the tubercles are frequently found arranged along the tap 

 root, often to a depth of 1.5 to 2 feet, penetrating the hard 

 subsoil, but only individual tubercles or small clusters are 

 found at such depths; the larger masses are found nearer 

 the surface in the looser soil. 



