DAMPING OFF. 257 



spore presents a very coarsely granular protoplasm the granules 

 rounded in form and closely packed together. 



Propagation also takes place by the production of non-motile 

 Conidia from monosporous sporangia. 



The conidia are oval or broadly obovate, colorless cells, with a 

 thin wall and measure from 15^. to 25 , u. in diameter. In germi- 

 nating, unless they are lying entirely immersed in water or in an 

 abundance of a water which may be on the surface of the pro- 

 thallium or on the soil, they do not form a mycelial tube directly. 

 A very short tube is formed and into this the protoplasm migrates 

 and causes the end of the short tube to swell out into an oval or 

 oblong vesicle or the vesicle may be separated from the conidium 

 by a constriction. This phase reminds one of the formation of 

 the zoospore vesicle in the species of Artotrogus. But the forma- 

 tion of this tube and of the vesicle does not take place so rapidly 

 as in Artotrogus, and the form of the vesicle is quite different and 

 varies considerably in form as well as in size, but the most marked 

 difference is that there is a firmer covering which appears to be 

 in the nature of a well defined wall around the protoplasmic 

 vesicle, while in Artotrogus there is only a protoplasmic mem- 

 brane. Here the analogy ceases for zoospores are not formed. 

 This cell is a germinal vesicle or proembryo, and from this pro- 

 embryo arises the slender tube which pierces the cell of the pro- 

 thallium and permits the parasite to enter. If the conidia are lying 

 in an abundance of water they will germinate and produce a tube 

 five to ten times the length of the diameter of the conidium. 

 This I have several times observed, but in no such case have I 

 observed the germ tube to enter a cell of the prothallium. Leitgeb 



Explanation of Plate IV. Completoria complens Iohde. 



Fig. 42 botryose cluster of plant body after being placed in water, the per- 

 ipheral cells germinating and forming long tubes. 



Fig. 43 plant body, some of the central cells forming resting spores, and 

 some of the peripheral ones developing conidia. 



Fig. 44 plant body in one cell of the host, the peripheral cells developing 

 tubes which penetrate adjacent cells of the prothallium. 



Fig. 45 two young plants in one cell of the host having entered from an 

 adjacent cell, early stages in the branching and development of the botryose 

 plant body are shown. 



All figures drawn with aid of the camera lucida and magnified 30 times 

 more than the scale. Scale, i millimeter. 



