Nebraska Forest l^nnyi. If 89 



that clearly differentiates the perithecium from the substance 

 of the stroma as in the Sphacriaceac. Otherwise the two fami- 

 lies are very similar. 



Dothidclla 



!n this genus the stroma is well developed and is discoiil or 

 ciTiise, thin and black. The asci contain eight ovoid or oblong, 

 uniseptate, hyaline spores. 



Dothidclla ulmca (Schw.) E. & E. 



The perithecia are imbedded in the leaf parenchyma either 

 singly or in clusters of 2-8 connected by stromatal cells, their 

 bases projecting and forming tuberculiform heaps on the upper 

 surface of the leaf, while their black papillate ostioles appear 

 through the ruptured epidermis on the lower side of the leaf. 

 The asci are oblong-cylindrical, 55-8 microns. The eight spores 

 become unequally 2-celled by a septum formed near one end. 

 The species is very common on the leaves of Ulmus arncricana. 

 Before the leaves have fallen the fungus is often very evident 

 because of the scattered areas composed of the black fungous 

 bodies. It is only after the leaves have lain on the ground 

 through the winter that the fungus is found to be mature, 

 although it is conspicuous long before leaf fall. In fact, the 

 external appearance in the spring is little different from that 

 in the fall. 



BASIDIOMYCETES 



There are few Basidiomycctes that attack the leaves of forest 

 trees in this state, a truth that holds quite generally for all places. 

 Among the most important leaf Basidiomycetes are the Rust 

 Fungi, forms that are very commonly classified with this group. 

 The following are the commonest rusts of Nebraska forst trees. 



Uredmaccae: 



The Urcdinaceae, or Rust Fungi, are obligate parasites pos- 

 sessing several forms of spores, one or a number of which may 

 be omitted from the life cycle of cc~tain species. These spore 

 forms are pycniospores, produced i i very small flask-shaped, 

 pycnidium-like receptacles called pycnia, and usually accompanied 

 by the next spore form, the aeciospcrcs, formed in the so-called 

 "'cluster cups" or aecia, of varying structure. The urecliniospores 

 come next in regular order, produced in sori or uredinia ; and 

 finally the teliospores, which upon germination, give rise to the 

 basidiospores complete the typical round of life so far as spore 

 formation is concerned. The teliospore is the form that is usually 

 present, no matter if a number of the other spore forms are 



