CAUSE AND NATURE OF CROWN-GALL 53 



mens were kept for a period of ten days in moist, crushed quartz 

 in a cool room and then placed in a moist chamber where they 

 could be observed daily. In every instance they were in as 

 fresh condition when placed in the moist chamber as when cut 

 from the trees. A vigorous growth of hypertrophied tissue had 

 formed in a number of places on the old galls, particularly on 

 the exposed surfaces where broken from the trees. If a gall in 

 this stage be cut into pieces, the sporangia will develope a 

 few days later on the cut surfaces. The first sporangium was 

 observed a few days after placing in the moist chamber, when 

 it had already ruptured. It is probable that the keeping of 

 the galls in a growing condition for some time after their re- 

 moval from the tree induces the plasmodia to fruit by cutting 

 off their food supply. Unlike all other slime-molds known to 

 me, this one fruits best if kept in the dark, a condition no doubt 

 arising from its parasitic habit on the roots of trees. 



The mature sporangium is nearly spherical, slightly broader 

 than high, and i millimeter or less in its greatest diameter. It 

 rests directly upon the tissue of the gall and is smooth and shining 

 under a hand lens. The color varies from dark, reddish yellow 

 to lighter. With transmitted light the peridium, or wall of the 

 sporangium, is deep orange. The outer surface is minutely 

 granular. The peridium is exceedingly brittle and breaks in 

 straight lines. As it is about to rupture to liberate the spores, 

 the outer surface dries more rapidly than the inner, causing it 

 to contract, creating a tension which finally causes the mem- 

 brane to rupture elastically. If a ripe sporangium be taken 

 from the moist chamber and quickly transferred to a slide and 

 viewed with a }■< or ~3 objective, the rupturing and the well- 

 marked outward curving of the fragments of the peridium may 

 be easily observed. The inner wall of the peridium is covered 

 with various-sized nodules of protoplasmic matter, varying from 

 less than % to more than 12 ,"■ in diameter. These nodules are 

 either imbedded in the wall or piled and massed together and 

 adherent to it. 



A fragmentary capillitium is attached to the walls of the 

 peridium, and is found to a limited extent associated with the 

 spores within. The threads of the capillitium are hollow, ir- 



