274 THE MONTHLY BULLETIN. 



indicates the presence of the fungus (Fig. 79). It is merely a question of time how 

 long the host can withstand the attack of the fungus it harbors. In the end the host 

 succumbs. With the death of the young pine the fungus plant itself dies off, but 

 before this happens, it has shed myriads of seciospores which are carried about by 

 the wind and assure the propagation of the fungus on the condition that they reach 

 a member of the Ribes family, to which currants and gooseberries belong. Unfortu- 

 nately the susceptible five-needle pines are generally associated with these plants, 

 of which only comparatively few seem to be resistant to the spores of the white pine 

 blister rust. 



With the shifting of the fungus from pine to Ribes a complete change in habits 

 and appearance takes place. The fungus which was strictly confined to the living 

 bark of young pines, now chooses the leaves of currants and gooseberries for its 

 domicile. vEeiospores landing on susceptible leaves germinate under favorable condi- 

 tions by sending out a very delicate germ tube, which grows into the leaf and here 

 again parasitizes the tissues as its mother plant had done in the pine. After this 

 young fungus has grown by taking its food from the tissues of the leaf, it is ready 

 to produce a third spore form, the so-called urediniospores. Their formation is first 

 signalled by the appearance of very small yellowish pustules on the underside of the 

 infected leaf, which soon break through the epidermis and begin to shed the yellow 

 spores (Fig. 80, B, C). These urediniospores (Fig. 81, No. 3), being able to infect 

 other leaves of currants and gooseberries, spread the fungus within a very short time 

 over a great many Ribes plants and thereby materially extend the radius of the 

 fungus within one summer. It only takes two weeks from the time the uredinio- 

 spores have landed on a Ribes leaf to produce another generation of urediniospores, 

 and as the production of these spores may continue throughout the summer, it is 

 readily seen that the fungus possesses in these spores a most effective means of 

 propagation and rapid dissemination. On the other hand, the urediniospores are 

 unable to infect white pine plants. Their life is strictly confined to currants and 

 gooseberries. With the death of the infected leaves and their dropping off in fall 

 the Ribes generation of the fungus also perishes, but again ample provision is made 

 for propagation. From the middle of summer on a fourth type of spores, the so- 

 called teliospores, follows the production of urediniospores on the underside of the 

 leaves. They appear to the naked eye as short hair-like horns or threads of a brown 

 color, which are composed of numerous teliospores firmly glued together (Fig. SO, D). 

 This type of spores is unable to infect Ribes leaves. Their function is to carry the 

 fungus back to five-needle pines. Since the telispores (Fig. 81, No. 4) are not 

 shed in form of spore dust, but remain united in the form of a small thread-like 

 structure, there would be little chance for their being carried bodily on to the bark 

 of pines. Another secondary type of spores, the so-called sporidia (Fig. 81, No. 5), 

 is necessary in order to reach the host. The very small sporidia are produced as a 

 result of the germination of the teliospores ; they are easily detached and are carried 

 off by the wind. When they land on the bark of a young pine its infection takes 

 place and the life cycle of Cronartium ribicola is completed. The result of the 

 infection of the young pine is again the blister rust, with first the swelling of the 

 stem, then the sweet pyenial drops and the typical white blister filled with orange- 

 colored spores (Fig. 81). 



It is on pine where the fungus shows itself from its worst side. The telial 

 (Cronartium) stage never kills a currant or gooseberry bush, although it is well 

 known that a heavy infection of Ribes prematurely kills individual leaves in consid- 

 erable number and thereby materially weakens the entire plant. Where currants 

 and gooseberries are cultivated for their fruit or for ornamental purposes the loss 

 from a heavy infection will make itself severely felt. But the real importance of 

 the Cronartium form on Ribes lies in the great facility with which the disease is 

 spread over large areas through the urediniospores and in the formation of the 

 teliospores which provides for the return of the fungus to the pine. 



The enormous damage it is able to inflict upon some of our most valuable timber 

 trees lifts the fungus from the rank of nuisance to that of an economically portentous 

 enemy, to be fought by all means. On five-needle pines the fungus is not content 

 with local injuries; it kills. It does not kill indiscriminately, but confines itself to 

 young trees or the younger parts of older trees. In Europe it appeared typically as 

 a disease of seedlings and in America it does its greatest damage to young trees up 

 to about thirty years of age, though 100-year-old trees also have been known to be 

 killed. The very fact that it attacks and destroys the future of the white pine forest 

 in the shape of seedlings makes it all the more insidious. Our country as a whole has 

 not yet learned to think seriously in future values. 



