THE ASCOSPORE AND OTHER FUNGI 253 



If you will look through a lens or the lower power of a 

 compound microscope at one of the leaves thus affected, 

 you will see that the whitish appearance is due to vast 

 numbers of tiny threads that run over the surface of the 

 leaf, interlacing in a most interesting fashion. You will 

 find that the brownish or blackish dots are well-developed 

 spore cases — technically called perithecia — often having 

 curious projections from the outer wall. You can probably 

 see these cases in all stages of growth, from the young 

 whitish ones to the mature blackish ones. 



If you place a few of the well-developed spore cases on 

 a glass slide in water, cover with another piece of glass, 

 and crush the walls, you will see the spores come out. 

 These spores are inclosed in smaller sackUke cases — the 

 ascL 



When the leaves fall in autumn, these black spore cases 

 fall with them, and the spores inside remain over winter to 

 start the disease anew in spring. For this reason they are 

 often called the winter spores. 



In spring or early summer the fungus threads get 

 started on the leaves. Unlike many other fungi, the 

 threads do not grow in or between the tissue cells of the 

 leaf, but they remain upon the outside and send curious 

 suckerlike projections in through the breathing pores of 

 the leaf to absorb food from the cells. 



During summer, especially before the development of 

 the winter spore cases, the affected leaves often have a 

 powdery appearance. This is due to the development of 

 millions of tiny white spores. Certain threads of the my- 

 celium grow out at right angles to the surface of the leaf, 

 and on their ends produce spores that serve for the spread 

 of the fungus during the warm months. These are called 

 summer spores or conidia. 



