OBSERVATIONS ON THE GENUS PTTHIUM. 501 



into separate blocks. This proceeded very rapidly to the 

 isolation of the blocks as zoospores. In three minutes 

 the stage shown at (i) was reached, the individual amoeboid 

 masses becoming quite active at 5.15, tumbling and rolling over 

 one another meanwhile in a most comical manner. At 5.20 

 their movements became more active, and the cilia appeared 

 (cf. fig. 14); and at 5.25 they were vigorously moving in the 

 extremely tenuous vesicle, the lashing of the two lateral cilia 

 becoming more and more rapid. One minute later, and the 

 vesicle burst suddenly, the active zoospores flitting off at 

 once in all directions. A distinct remnant of the lower third 

 of the vesicle remained attached to the apex of the widely open 

 beak {k). The upper parts appeared to become completely 

 dissolved in the water. 



As an illustration of the other mode of behaviour of the 

 zoosporangia, the various stages shown in fig. 15 may suffice. 

 Two zoosporangia, which had remained dormant for many 

 months in a cool cellar, were each observed to put forth the 

 pale swelling at the apex of the beak, as described above. In- 

 stead of forming the vesicular swelling and zoospores, how- 

 ever, the pale apex became prolonged into a tube, the vacuoles 

 in the sporangium increasing meanwhile as the contents 

 passed slowly forwards. To give an idea of the rate of growth 

 of such a germinal tube, the changes at the apex were observed, 

 as figured (c to i). The germinating sporangium or coni- 

 dium (fig. 15 c) was drawn at 2.50; at 3.2 the apex had 

 swollen and perceptibly elongated (d) ; fig. e represents the 

 condition four minutes later; f, after another two minutes; ff, 

 after four more minutes — i.e., at 3.12 o'clock ; h was drawn at 

 3.20; and ^, at four o'clock. Although it may be convenient 

 to distinguish these germinating bodies as conidia, it cannot 

 be maintained that any perceptible differences between them 

 and zoosporangia are observable until germination occurs. 

 Whether the behaviour depends on internal or external influ- 

 ences cannot be decided at present, though much may perhaps 

 be said for the latter view. 



As already stated, the zoosporangia may germinate either 



VOL. XXIII. NEW SER, L L 



