1L>L' THK AMKKICAN MOKTllLV [May, 



jjiallinijit. I'lic supply of luitriincnt lliiis bciiiij cut oil" from the 

 tcri)nn;il portion i>l'tlic twij;, tloath of that portion roUowoil. 



Scalftl ill the oriijinal diseased areas, whetlier extetulin<; partly 

 or entirely around the stem, are minute bhick elevated points 

 wliich can l>e seen with the unaiile<l eye. Figure i </ ami /» rep- 

 resent portions of twij^s. </ with the iliseased area extendinjj; partly 

 around the stem, while h is j^irdletl. In the diseased areas are 

 shown these small black elevations. The disease is {produced by 

 a f"unj,'us u hich «jrows within tiie stem. These black elevated 

 points are centres where pustules of the t"ungus are developed 

 contaiiiiuL; its ie|)roducti\ e bodies, oi spores. 



Section Across one of the Pustules of the Fungus. — 

 Fijjure 2 represents a very thin section across one ot' these pustules, 

 maj^nilied to show the structure of the pustule and the form of 

 the spores. The jjrowth of the pustule has ruptured tiic epider- 

 mis of the stem. In the openinj; between the broken parts of 

 the epidermis are shown some of the spores. Beneath these are 

 numerous parallel short fruitinj; threads, or basidia of tlie funj^us, 

 at the end of which the spores are ileveloped. The basidia can 

 be seen to arise from the blackened stroma of the fun<^us, which 

 consists of quite a compact association of irregjular cells. The 

 black color of the ]iustules comes tVoni the stroma. 



Method of Separation of the Fungus. — To study the de- 

 velopment of the fun<;us it was necessary to separate it from other 

 common forms of funj^i as well as bacteria which always find a 

 lodjrnient in and upon dead plant tissue. Since all these forms 

 are microscopic the .separation involves a method of procedure 

 familiar only to specialists, and as such beautiful results were 

 reached in the separation of this fun<i;us it suggested a graphic 

 pre.sentation of the method in connection with the study. The 

 method used was the same as that which Koch developed so ad- 

 miraV)ly for the separation of bacteria, and consists in tliedilution 

 of the organisms in several quantities of a warm lirjuid substance 

 which, when spread out in a thin layer and cooled, solidifies and 

 holds each germ firmly fixed at one point in the dilution. 'I'his 

 substiince is usually some gelatinous base, as gelatin, or agar- 

 agar, containing beef broth and peptone to furnish food for the 

 organisms. In a few days after cooling the dilutions in the thin 

 layer each germ by growth has produced a colony which can be 

 seen with the unaided eve. 



Three glass tubes containing .i small quantity of liquid nutrient 

 agar-agar were placed in the water bath at 43° centigrade. This 

 temperature is sufficient to keep the agar liquid, while it is not 

 hot enough to kill the organisms. Now several thin shavings 

 through the fungus pustules on the stem of the jjrivet were trans- 

 ferred to tube Xo. I. Tliis was shaken gently to distribute the 

 germs evenly through the liquid. Now a small quantity of the 

 liquid in No. 1 containing the germs was transferred to tube No. 

 2, making the second dilution, and from No. 2 to No 3, making 



