138 Minnesota Plant Diseases, 



tance economically 'because of its numerous diseases. The 

 sphere fungi are close relatives of the dung fungi and build 

 similar sac-capsules which are usually tiny spheres. These are 

 generally formed singly or are sometimes grouped on a mycelial 

 cushion somewhat similar to black knot. The sac-capsules are 

 very often microscopically small. These fungi are remarkable 

 for the great numbers and variety of accessory spores produced. 

 Most of the so-called imperfect fungi are undoubtedly merely 

 accessory spore-forms of these fungi. Although the group is a 

 large one the sac-capsules agree to a remarkable extent in their 

 essential structures and vary only in such characters as 

 hairiness, wall structure, shape and structure of sacs and spores 

 and other minor details. The accessory spores are some- 

 times found on simple erect threads, from which they are 

 pinched off in regular succession. In other cases the spore- 

 producing threads may be bunched together into cushions, and 

 in still other cases they may be formed in cavities or cases, 

 quite similar to those of many- sac-cases in appearance, though, 

 of course, they do not contain sacs. Moreover, such accessory 

 spores may vary in number and arrangement of cells. They 

 may consist of a single cell or of a definite or indefinite number, 

 which may be built up into a net-shaped complex or into long 

 strings. On the characters of the sac-capsule structure and 

 opening, on sac-spore shape, etc., and on the grouping, struc- 

 ture, etc., of the accessory spores, an elaborate artificial classi- 

 fication of the group has been built up. This system, though 

 artificial, is nevertheless useful as a framework for collecting 

 and describing information about this vast group of plants. 



The sphere fungi inhabit almost all plant parts though they 

 may be said to be most numerous upon the leaves of their hosts. 

 They are also very abundant on herbaceous stems and may 

 even be found on woody stems, on timbers, roots and fruits. 

 Many needle-cast diseases of cone-bearing plants, as pines, are 

 caused by sphere fungi. Certain root diseases of vines and 

 other plants, the leaf spot disease of strawberry and many other 

 so-called leaf-spot diseases are due to sphere fungi. Apple 

 scabs on leaves and fruits and many other diseases of cultivated 

 plants might be cited as further examples. In fact the great 

 majority of plants harbor one or more of these parasites. They 



