58 



BOTANY. 



are formed by the ends of the filaments swelling up and becoming con- 

 stricted, so as to form an oval spore, which is then cut off by a wall. The 

 portion of the filament immediately below acts in the same way, and the 

 process is repeated until a chain of half a dozen or more may be produced, 

 the lowest one being always the last formed. When ripe, the spores are 

 separated by a thin neck, and become very easily broken off. 



In order to follow their germination it is only necessary to place a few 

 leaves with fresh patches of the fungus under a bell jar or tumbler, 

 inverted over a dish full of water, so as to keep the air within saturated 

 with moisture, but taking care to keep the leaves out of the water. After 



an. 



FIG. 33. A, leaf of pigweed (Amarantus) , with spots of white rust (c), one- 

 half natural size. B, non-sexual spores (conidia). C, the same germinat- 

 ing. D, zoospores. E, germinating zoospores. sp. the spore. F, young. 

 G, mature sexual organs. In G, the tube may be seen connecting the 

 antheridium (an.), with the egg cell (o). H, a ripe resting spore still 

 surrounded by the wall of the oogonium. 7, a part of a filament of the 

 fungus, showing its irregular form. All x 300. 



about twenty-four hours, if some of the spores are scraped off and 

 mounted in water, they will germinate in the course of an hour or so. The 

 contents divide into about eight parts, which escape from the top of the 

 spore, which at this time projects as a little papilla. On escaping, each 

 mass of protoplasm swims away as a zoospore, with two extremely delicate 

 cilia. After a short time it comes to rest, and, after developing a thin 

 cell wall, germinates by sending out one or two filaments (Fig. 33, (7, E). 

 Under normal conditions the spores probably germinate when the leaves 

 are wet, and the filaments enter the plant through the breathing pores on 



