264 PYTHIUM DE BARYANUM. 



present in mature sporangia but disappears shortly before zoospore- 

 formation. The latter process is exactly similar to that of other 

 species of the genus, the sporangial contents escaping into a thin- 

 walled vesicle formed at the apex of the beak and maturation of 

 the zoospores taking place within this vesicle (Figs. 11 and 12). 

 Five to eighteen or more zoospores may be given by a sporangium. 

 The zoospores are still figured, by a curious case of persistence of 

 error, in most text-books, as being pear-shaped and uni-ciliate. 

 Even in a recent original study 1 , Hesse's old figures of 1874 have 

 been copied. As the fungus is prescribed as a type in the botany 

 syllabus of many institutions and is included in several popular 

 text-books, it is as well to be accurate on this point. When first 

 liberated the zoospore is longer than broad, the two longer sides 

 being unequal in length and the shorter of the two sometimes de- 

 pressed in the centre, the shape being like a bean somewhat flat- 

 tened vertically, and with one end more pointed than the other 

 (Fig. 13). From the hollow or hilum two cilia arise and diverge ; 

 by their movements the zoospore swims rapidly. As it slows down 

 it becomes shorter and thicker, the two cilia being still distinct. 

 When it comes to rest the cilia are retracted, but their position is 

 still marked for a time by two droplets, perhaps of a fatty nature 

 (Fig. 14). No case was seen of any tendency of the zoospores to 

 divide into two 1-ciliate secondary zoospores, as described by 

 Atkinson' 2 in Pythium intermedium. It is extremely probable, 

 therefore, that Hesse's figures were based on erroneous observations, 

 the more so that they have not been confirmed by others since. The 

 type of zoospore in P. de Baryanum is that normal for the Peronos- 

 poracew as a whole. 



On germination the zoospore emits usually a single germ- tube, 

 which grows to a considerable length and branches at the extremity. 

 It is sometimes septate (Fig. 15). 



1 Peters, L. Eine haiifige Steoklingskrankheit der Pelargonien. Oartenflora, 1910, Taf. 

 15S2. 



2 Atkinson, G. F. " Damping off." Cornell University Agric. Exper. Stat. Bull. 94, 

 1895. 



