i ' ' Damping Off. 381 



case which came under my observation shows clearly the necessity 

 for the aerial development of the sporangia in the formation 

 of the conidia in this plant. In mounting an affected pro- 

 thallium in water for examination I discovered a partly formed 

 sporangium which projected out into the cavity of an old and 

 •emptied ruptured cell. In the growing condition of the prothallia 

 in this case they were somewhat crowded so that they stood, more 

 or less erect. The sporangium then in growing also in an erect 

 position away from the moisture would be directed into the empty 

 cell above. Placing this prothallium in a horizontal position on 

 the glass slip in a small quantity of water would immerse the 

 sporangium in the water, or partly so. All of the water was then 

 drawn off except just a sufficient amount to prevent the prothal- 

 lium and fungus from drying and the preparation was placed in 

 a moist chamber in order that from time to time it might be 

 examined to watch the development of the sporangium. This stage 

 of the sporangium is represented in Fig. 43. No farther develop- 

 ment of this sporangium took place. But just at the base of 

 the stalk another one began to be thrown up in a position per- 

 pendicular to this prostrate one. As the new one increased in 

 height the old one gradually lost the protoplasm both from the 

 forming sporangium and the stalk. In the course of four to five 

 hours the sporangium was mature and the conidium ejected, when the 

 sporangium and stalk collapsed and remained as a flabby membrane 

 attached to the wall of the old stalk and sporangium which was still 

 in the water and which still remained intact. 



The conidium is capable of germinating immediately when there 

 is sufficient moisture and the behavior seems to be manifested in 

 three different ways according to the amount of moisture, or in 

 some cases perhaps according to the proximity of the host. If the 

 spore is entirely immersed in water a long slender germ tube is put 

 forth similar to the tube which is emitted from the terminal cells 

 of the botryose body of a vegetatively mature plant. Where less 

 water is present the conidium germinates by developing a germinal 

 vesicle, or proembryo as described above. 



From the inner face, the one lying next the prothallium cell, 

 of the broader end of the proembryo, a minute tube is thrust out 

 which pierces the cell wall of the host and grows out to the center 

 of the cell lumen where in the ordinary way it enlarges into the 

 first ovoid body of the new plant (Figs. 38, 40). In other cases 



