24 MASS. EXPERIMENT STATION BULLETIN 183. 



Methods of Inoculation. — (a) Stems wounded, inoculated with agar in which 

 the fungus was growing, kept moist several days with moist cotton, {b) Same as 

 (a), but the plants not wounded, (c) Wounded, spores sprayed over the plants 

 with an atomizer, and kept for several days under a bell jar. (d) Same as (c), 

 but plants not wounded. All these methods were controlled by checks treated in 

 the same way except for applying the fungus. 



Typical cankers were produced by all four methods of inoculation. 

 The shortest incubation period — time between inoculation and first 

 appearance of symptoms — was four days on the wounded plants and 

 five days on the unwounded ones. The rate of development of the canker 

 after it first appears varies greatly. On some plants which were first 

 wounded and kept under bell jars the cankers were over a centimeter 

 across in two weeks, but if the bell jars were removed and the humidity 

 of the air diminished, the cankers grew very slowly. Small aerial cankers 

 usually soon stop growing altogether unless several of them occur close to- 

 gether, or unless they are kept very moist. Crown cankers grow more 

 rapidly than cankers higher up, but their rate of growth becomes de- 

 cidedly slower as they advance above the surface of the soil. 



4. Reisolations were very readily made from a number of the cankers 

 produced by artificial inoculation. The fungus was obtained in pure 

 culture, and easily identified by its cultural and morphological characters 

 as Cylindrocladium scoparium. 



Injection Court. 

 The artificial inoculations described above indicate that a wound is 

 not necessary for infection. All observations indicate, however, that a 

 wound is a very favorable infection court. A great many of the basal 

 cankers start from the union of stock and scion; aerial cankers from the 

 cut surfaces of stubs and from various bruises made by tools, etc. Even 

 where no wound appeared, it seemed possible that there might be small 

 wounds not readily visible to the naked eye. In order to determine 

 whether such was the case, and if not, to determine whether any natural 

 openings in the epidermis serve as infection courts, artificial inoculations 

 were made by spraying spores with an atomizer on what, as far as could 

 be seen with the naked eye, seemed to be perfectly healthy stems. As 

 soon as canlcers began to appear they were cut out, fixed, imbedded in 

 paraffin, cut into serial sections and stained. Twenty-four cankers 

 varying from the size of a pin point to 2 millimeters in diameter were 

 used and cut serially to a thickness of 8 /i. In no case was any wound 

 through the epidermis discovered. But in every case a stomate was 

 located directly at or very near the center of the canker. In the larger 

 cankers there were several stomates, and it was not always possible to 

 determine the point of entry. In the smaller ones, however, only one 

 was present, and it was always approximately at the center. A number 

 of infections were also discovered which were so small that they had not 



