248 THYTOPHTHORA MEADII n. fjp. ON HEVEA BRASILTENSIS 



observed the germination of sporangia many times fiom material got from 

 cultures and from nature. When water is not present in sufficient volume 

 the sporangium does not discharge zoospoics, but germinates as a conidium 

 by putting forth one or more geim-tubes, usually through the apical opening 

 but occasionally through the wall. This is seen to srme small extent even 

 in water-cultures ; it can be made to occur in a culture where care is taken to 

 withdraw the water of condensation from the culture medium, audit occurs 

 to a very large extent when rain does not fall on infected fruits for a day or 

 so after they have begun to form sporangia on the surface in large numbers 

 as they often do. The zoospores usually swim away individually, but not 

 infrequently two or more remain attached or they may have their cilia 

 entangled and gyrate round one another as they move along. The zoospores 

 are kidney-shaped and vary from 7 to 10-5/x having an average measurement 

 of 8-7 fi. Each has a nucleus and sometimes a vacuole . They have two 

 cilia. Sometimes a zoospore has only one cilium, but whether this is due to its 

 having lost one which may have been entang'ed with that of another zoospore 

 and become detached while they struggle together, or whether a second cilium 

 did not develop I do not know as I have been unable to tiace the origin and 

 development of the cilia. The fact that cilia have been found lying loose in the 

 preparation suggests the former possibility. The ciha are inserted at or near 

 the hilum. Sometimes they appear to be attached near the two ends of the 

 zoospore, but this appearance I feel sure is due to slight overstaining and the 

 difficulty of tracing the delicate ciUa to their points of origin. In some pre- 

 parations the cilia, though becoming clear of the zoospore at its ends, can be 

 traced distinctly across the zoospore to its hilum. The ciha vary in length 

 from 16 to 23 G//. the average being 19/m, and the pairs are of slightly unequal 

 length. When the zoospores come to rest as they do within half an hour they 

 become spherical, surround themselves wath a thin cell-wall, and germinate 

 in from 10 minutes to an hour by sending forth one or more germ-tubes. 

 Sometimes the tube immediately forms another sporangium which may 

 discharge zoospores in the ordinary way or may germinate as a conidium ; 

 usually how ever it forms a hypha of considerable length with several branches. 

 Germ-tubes have been observed to extend from 40 to 80 fi in 24 hours, while the 

 extreme growth in length in that time was 236/ut of which a length of 28/x from 

 the tip was filled w4th protoplasm. In a recent culture, however, from an 

 infected fruit lengths of 40 to 270/x were measured in 4 hours. Though as a 

 rule no transverse wall is formed behind the retreating protoplasm, yet occa- 

 sionally the part with protoplasmic contents is cut off from the remaining 

 empty part by a cell-wall even at this early stage, 



