114 STUDY OF COjVIMON PLANTS. 



3. On the opposite (upper) side of the leaf, and par- 

 tially sunk in its tissue, are usually found some 

 minute bodies which project in a sort of pencil, or 

 hairy cone, beyond its surface. These are spermo- 

 gonia. That they belong to the same fungus 

 is proven by following the mycelium continu- 

 ously from an secidium fruit to a spermogonium. 

 Their structure is made out with more difficulty, 

 but it may be observed that it resembles in 

 some important particulars that of the secidium, 

 in that it is hollow and produces extremely minute 

 spores, spermatia, which are borne on stalks, basidia, 

 from which they afterwards separate. The tuft of 

 hair-like bodies projecting beyond the leaf are the 

 paraphyses. They surround the narrow opening, 

 ostiole, through which the spermatia escape. 



Note. —The observation of the details of structure of the 

 spermogonium is difficult until the student has had considerable 

 practice, and it may be desirable to omit its study unless the 

 material is particularly favorable. The other parts of the fun- 

 gus, however, present no special difficulties. 



4. Notice the effect of the fungus on the barberry leaf. 



VII. Write a careful summary of your observations of 

 wheat rust, including what you have seen of its occurrence 

 on different hosts, the structure of the mycelium and its 

 relation to the tissues in which it occurs, the different 

 kinds of spores and the season at which they are produced, 

 and the effect of the fungus on its hosts. 



Note. — It is not possible in the short time given to its study to demon- 

 strate fully the cycle of development of this fungus, but its most impor- 

 tant features are easily observed. It should be stated, however, that 

 notwithstanding the repeated and long-continued investigation that has 

 been devoted to it, largely on account of its economical importance, it is 



