173 
of in the compact growth, and is only plainly visible in the sur- 
face. 
The internal structure of the gall differs but little in the rela- 
tion of the different tissue systems from that of the normal root. 
The central cylinder is present surrounded by an abnormally 
great development of parenchymatous tissue, which is surrounded 
- by the corky layer. The parenchymatous tissue harbors the 
parasite. 
In Ceanothus Americanus there is a narrow zone of paren- 
chymatous cells, immediately surrounding the central cylinder, 
usually free from the parasite and made up of nearly isodiametric 
cells. Bordering this is a broad zone of parenchymatous tissue 
of large cells quite variable in size and shape. The cells contain- 
ing the parasite are usually considerably larger than the others. 
Frequently all the cells of this zone viewed in cross section are 
elongated radially. In Alnus serrulata the cells containing the 
fungus are but little if any larger than the other parenchymatous 
cells, and the radial elongation of the cells is rarely observed. 
The observation and determination of the fungus is not so easy 
as in the galls on Ceanothus Americanus, because of other sub- 
stances which obscure it. 
The fungus when mature forms compact botryoid clusters in 
the affected parenchymatous cells of the gall, the central portion 
being composed of a complexly-branched mass of threads bearing 
at their ends on the periphery of the mass the globose sporangia. 
A brief résumé of the leading views concerning these galls 
from a historical standpoint will be of interest in connection with 
a description of the fungus. 
Meyen* considered them to be parasites growing upon the 
roots of A/nus, having a habit in this respect similar to members 
of the Balanophoracez or Orobanchacez, though lower in devel- 
opment and systematic position. 
Schacht at first regarded them as normal growths of the 
roots. Later} he held the view that they were abnormal gr owths, 
but offered no theory as to their cause. 
* Ueber das Hervorwachsen parasitischer Gewiichse, etc.. 
“aogte from Woronin, Mem. d. l’Acad. Imp. d. Sciences Vile, 
+ Flora, 1853, S. 10, 11. Quoted from Wor. I. c. 
Der Baum, 1860, S. 172-174. Quoted from Wor, 
Flora, 1829, S. 49. 
Tome X., No, 6, 
