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duced by G. globosum have small elevated areas, or mounds (fig 145). From these raised areas the telial horns appear in the following spring.

The telial horns are wedged-shaped and are chestnut brown in color (fig. 146). Scars of the horns of former seasons are often apparent

between the horns on old galls. When the warm spring rains occur, the protrusions gelatinize and enlarge to about double their normal size (fig. 147). These horns dry and drop off at the end of the fruiting season, but the galls may continue to live and bear spores

for seasons.

The old galls turn broun and become roughened on the surface due to the scars of the telial horns.

several

On quince A yellow spot, such as characterizes the lesions caused by G. Juniperivirginianae on the apple leaf, is formed by G. glo bosum on quince foliage. The pycnia and the aecia are likewise formed on the upper and the lower surface of the leaf, re

spectively. To all exFig. 146. GALL CAUSED BY GYMNOSPORANGIUM GLOBOSUM

ternal The typical telial horns are shown prior to gelatinization

the appearances

symptoms are the same as those described for G. Juni peri-virginianaeon apple foliage.

On pear

Stewart (1910) states that infected spots on the upper surface of pear leaves are dark brown or nearly black in color, with a conspicuous red

border. Spots on the under surface are of the same dark color but have no red border. Aecia are produced in the largest lesions and also on the infected leaf petioles. In many cases the rust spots are arranged in

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two irregular row's, one on each side of the midrib, giving the appearance of infection having occurred before the leaves were unfolded.

In 1910 Stewart observed that infected fruits were still clinging to the trees on

The June 15, although they were usually less than half the normal size.

fruit is often deformed and bears a circular, flattened, black lesion devoid of aecia near its base. Aecia are produced rarely.

On Crataegus The lesion produced by G. globosum on Crataegus leaves is almost identical with the rust lesions on apple foliage. The red border about the margin of the spot is not so common, however, and the aecia are rarely arranged in the form of a circle (fig. 148).

The twigs of Crataegus are not commonly affected by this rust, but an occasional twig infection has been observed. The lesion is yellow,

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similar to that on the leaf, but practically no swelling of the twig is apparent. Pycnia are produced in this discolored area, followed later by aecia (fig. 149).

when the aeciospores are being dispersed.

Infected fruits have been found, but these are not common. Here again a yellow spot is formed but little or no hypertrophy results. The pycnia and the aecia follow in the same lesion.

AECIA OF GYMNOSPORANGIUM GLOBOSUM
The aecia are developing from the under surface of Crataegus leaves. The stem

and the leaf petiole are also affected

ETIOLOGY

Nomenclature The fungus now known as G. globosum was first named by Parlow in 1880. He gave it the name G. fuscum var. globosum, but later (Farlow, 1880) changed the name to G. globosum.

Life history The details of the life cycle of this species are almost identical with those of G. Juniperi-virginianae. The aeciospores of the two species mature at approximately the same time. The time of infection of the cedar has not been determined, but it is presumably during the period

[graphic]

FIG. 149.

Rust-infected Crataegus leaves were collected on September 26, 1914. and exposed to the weather in a wire screen. At this time aeciospores taken from these leaves failed to germinate. Subsequent tests were made and germination was obtained until December 15, but all attempts to germinate these spores after this date failed.

Since aeciospores will germinate during and even later than the time of their dispersal, the writer sees no reason for assuming that infection does not take place until the following spring, as Reed and Crabill assume for G. Juniperi-virginianae. Although the penetration of the germ tube has never been observed, there is but little doubt that it enters the stomata. The mycelium develops within the cedar leaf for a period of from ten to twelve months before any sign of infection becomes apparent.

Telial stage

Development of telial horns.- The mycelium of this species is practically identical with that of G. Juniperi-virginianae and there is almost a complete absence of haustoria in the young galls. The telial horns are developed from a stromatic layer in the same manner as are those of G. Juniperi-virginianae. They begin to develop in the autumn but it is not until early the next spring that they become far enough advanced to penetrate the surface of the gall.

In the spring of 1915 the epidermis over the papillae had begun to break open on March 29, while at that time no evidence of this breaking could be found on the galls of G. Juni peri-virginianae. The telial horns were apparent on April 10. No growth in plant life was evident at that time and there was still considerable ice and snow on the ground. Spores capable of germination were present in these tentacles on April 15.

The telial horns continue to increase in size so that when gelatinization first takes place they may be from 1.5 to 3 millimeters thick by from 2 to 5 millimeters broad at the base and from 6 to 12 millimeters high. The number of horns on a gall varies from one to one hundred or more. They are distributed on the gall unevenly and are chestnut brown in color. Instead of standing singly they may coalesce and form a continuous band around the gall. The horns of G. Juni peri-virginianae have never been seen to fuse in this way.

The first gelatinization period usually coincides with the first warm rain period after the horns are protruded, and the number of times this process may occur during a season varies greatly. In 1914 the horns gelatinized four times and fell off on May 20, while in 1915 twelve such periods were recorded before the horns became dry on June 2.

The telial horns of this species may be more than double in size when swollen, and are then thinner in consistency than the jelly-like horns of

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