224 Transactions British Mycological Society. 



the experiment. Pycnospores evidently can infect the clover 

 host more readily than conidia. Leaves infected by pycnospores 

 after being fixed (alcohol and formalin), microtomed, and stained 

 (haematoxylin), were examined for signs of infection and it was 

 seen that germ tubes usually entered the host by penetrating the 

 cuticle of the leaf but in one instance a germ tube was seen 

 entering through a stoma. 



It is evident that infection does not spread rapidly over large 

 areas, so the question arises as to how the conidia and pycno- 

 spores are distributed. The conidia are large and heavy and 

 after falling cling somewhat persistently about the bases of the 

 conidiophores. It is therefore concluded that they are not 

 dispersed to any great extent by wind, although this is probably 

 the chief means by which they are scattered. Rain will wash 

 them about on the same leaf, but not often on to other leaves, 

 so that there are very small chances of an epidemic of this 

 fungus caused by conidia. In view of the enormous numbers of 

 pycnospores which are produced, hundreds of thousands in 

 one pycnidium, these might be expected to cause a rapid spread 

 of the disease. The pycnospores are considerably smaller and 

 much lighter than the conidia, and could easily be carried about 

 by the wind. But the spores are for the most part discharged 

 only in tendril form suffused with mucilage, and only into a 

 humid atmosphere, hence they are not in a condition to be easily 

 carried by the wind; however, when dry, the wind might act 

 as an agent of dispersal. Water freely disperses the spores, and 

 in this way they are washed from one leaf to another, but even 

 so, the area affected can only be small and very restricted, and 

 uninfected plants a few yards away are quite likely to escape 

 infection. On this account it is not surprising that the disease 

 does not spread rapidly. 



3. Ascophorous stage. It had been noticed that after the 

 pycnidial stage had reached maturity, the clover leaves withered, 

 and finally fell to the ground, where they rotted or were dragged 

 into the soil by worms, etc. As a result it was impossible to 

 study the further development of the stromata until means were 

 taken to prevent the disappearance of decaying leaves. 



Leaves showing the pycnidial stage of the fungus were placed 

 between large ivy leaves, and buried in soil in flower pots. Ivy 

 leaves were used because they rot very slowly, and it was thought 

 that even if the clover leaves rotted away completely, the 

 black stromata might be found lying between the ivy leaves, 

 and that though the stromata are so minute (-2-1 mm.) they 

 would not be lost in the soil. These pots were placed out-of- 

 doors, so as to be under natural conditions. After a fortnight, 

 one of the pots was brought into the house for eleven days, and 



