12 FARMERS' BULLETIN 742. 



(fig. 5). After the swelling of the bark has become apparent upon 

 an infected pine, the healthy green color of the bark on the affected 

 areas is apt to change to a reddish and yellowish color. On the 

 yellowest patches, the parasite pushes forth, through tiny openings 

 in the bark, small drops of a clear, sweet-tasting fluid (fig. 5) . This 

 is not pitch. In it, if examined with a microscope, one finds immense 

 numbers of tiny spore bodies. These may be found early in the 

 spring before the formation of the blisters described below, or they 

 may occur apparently at almost any season in late summer and fall. 

 What the function of these tiny s^>ore bodies may be, nobody knows. 

 They occur in a considerable number of closely related parasites, but 

 are not known to reproduce the disease in any way. They are simply 

 indicators of the disease. They are known as pycnospore-s. Shortly 

 after the pycnospores are produced, from the latter part of April 

 until about the middle of June, the real fruiting bodies push their 

 way through the swollen tissues of the bark until they become 

 visible on the exterior. Here, they first appear like white blisters 

 as large as a child's finger nail. After a brief time, the top of the 

 white membrane breaks loose and falls off. Then it is seen that this 

 membrane surrounds a mass of bright-yellow powder (fig. 1 and 

 PL I, A). Each grain of this powder is a spore, capable of repro- 

 ducing the disease. These spores can not, however, infect the pines, 

 but can only attack leaves of currants or gooseberries. After the 

 parasite has fruited once upon the pine, the latter may remain alive 

 until the next year (fig. 1). In most cases, however, the bark is 

 killed completely around the affected part, thus girdling it (figs. 1 

 and 2) . In most cases this means the immediate death of the outer 

 or upper portion of the branch or trunk. Some trees, however, 

 struggle along for a number of years, and sometimes even for 15 or 

 20 years. In such cases the parasite sends out a new crop of spores 

 each spring to infect any currants or gooseberries that may be in 

 the vicinity. These yellow spores produced in the blisters in the 

 pine bark are known as aeciospores, or Peridermium spores. 



The Peridermium spores above described are very easily blown 

 about by the wind, and undoubtedly they are distributed mostly in 

 this way. As above indicated, if one of them falls upon a leaf of a 

 currant or gooseberry it is able to attack that leaf (fig. 4, a and I) . 

 There must, however, be present a certain amount of moisture for 

 the spore to germinate. Unless the weather is very dry, the neces- 

 sary amount of moisture is usually present. In the presence of 

 suitable moisture the tiny spore sprouts somewhat like a grain of 

 corn. It sends its rootlike germ tube into the soft tissues of the 

 currant leaf, and there it spreads within the leaf tissues until it has 

 attained a certain amount of strength and has parasitized a small 

 area of the leaf tissue. Temperature conditions control the rapidity 



