Parasitic Fungi of Illinois. 1 53 



taneously, or nearly so, on the infected area of the host, but 

 most often on the opposite sides, if of a leaf. In some cases 

 the other fruit forms subsequently develop in the order named 

 upon the same mycelium, but in others only on a new mycelium 

 produced from the germination of the aecidium spores, and 

 either on the same or different hosts, according to the habit of 

 the species. These alternations may be best understood by 

 consulting what is said under the genus Puccinia. 



But this full series of forms is not found in all the spe- 

 cies. Indeed, there are comparatively few which are really 

 known to have in their regular course of development all the 

 stages as necessary requirements of growth. In a few instances 

 it is known that species, which under some circumstances have 

 this or that form produced, may, under other circumstances, 

 perpetuate themselves though one or more forms are omitted. 

 In very many cases the genetic connection of different fruit 

 forms has not been satisfactorily made out; but contributions 

 to knowledge of this kind are from time to time gained, and 

 through the interest now taken in the matter more rapid ad- 

 vance may be expected in the future. For this purpose artifi- 

 cial cultures, with the most painstaking care to avoid mistakes, 

 are required. The spores must be placed on the proper host 

 under proper conditions, and the development carefully fol- 

 lowed through the season. It is believed that in some specie 

 only teleutospores are produced, in others only uredo and teleu- 

 toforms, and these from the same mycelium; in still others only 

 aecidium and teleutoforms. The office of the spermogonia has 

 not been conclusively ascertained. Cornu, of France has seen 

 the spermatia from them germinate in certain nutritive fluids, 

 but not in water, and he has supposed they may under certain 

 conditions reproduce the plants like other spores. Many have 

 attributed to them sexual functions, but the proof is unsatis- 

 factory. It has been observed that some spermogonia are fra- 

 grant, and insects are known to visit them, hence the inference 

 that the special office may be for dissemination. 



In most cases the mycelium of these plants wanders little 

 from the point of penetration of the host tissues in this 

 strikingly differing from the usual growth of the species of 

 Ustilagimcp and some other groups of fungus parasites. In 



