INTRODUCTION 35 



by the formation in culture of large amounts of toxic metabolic products. 

 Emerson and Cantino (1948) have described their isolation of Blasto- 

 cladia pringsheimii and B. ramosa, species common in nature on rosa- 

 ceous fruits where they form dense pustules of plants mixed with swarms 

 of bacteria, as follows: 



(1) Wash the fruit for several minutes under a strong stream of tap water 

 to displace as much debris and slime as possible. Many of the looser, super- 

 ficial masses of bacteria are effectively removed in this manner, while the 

 plants of Blastocladia, being firmly attached by well-developed basal rhizoids, 

 are not dislodged or appreciably injured. (2) Pick off three or four healthy 

 pustules and place them in a Petii dish of sterile water. (3) Using small 

 needles under a wide-field dissecting microscope, tease apart one or two 

 of the pustules bearing the largest number of mature healthy zoosporan- 

 gia. Individual plants, sporangium-bearing branches, and even dislodged 

 but intact sporangia can be separated in this way, and at the same time 

 clouds or adhering masses of bacteria are released from between the fungal 

 hyphae. (4) With fine needle-tweezers, transfer several of the plant-fragments 

 bearing uninjured zoosporangia to a second, smaller (ca. 5 cm. diameter) 

 Petri dish containing sterile water. With the mirror of the dissecting mi- 

 croscope adjusted to give a partial dark field or Tyndall-efifect, the largest 

 swarms of bacteria can readily be detected and avoided while portions of the 

 fungus bearing a minimum of contaminants are removed. If intact sporan- 

 gia have become detached, they can be picked up in the capillary stream 

 of a sterile micropipette and likewise transferred to another dish of sterile 

 water. If necessary the washing process can be repeated two or three 

 times until the material appears relatively free from bacteria. (5) The plant- 

 fragments and sporangia are now allowed to remain uniil the discharge of 



zoospores begins The material should be examined every few minutes 



to detect the emergence of spores at the earliest opportunity.(6) At this stage 

 it is worth while to plate out some of the spores directly without further 

 handling, since adequate separation from bacteria may already have been 

 achieved. In most instances, however, it is necessary to wash the spores 

 through one or two dishes of sterile water. The zoospores of Blastocladia 

 are about 10 \i in diameter, and single ones can be readily detected with 

 a high power dissecting microscope giving a magnification of at least 60 x , 

 especially if the lighting is adjusted as described above in item 4. With a 

 sterile Pasteur-pipette, made of soft glass and pulled out into a microcapillary 

 at the tip (20-50 \l internal bore), zoospores, singly or in groups, can easily 

 be picked up in the capillary stream which develops when the pipette is placed 

 in water. If the mouth of a small capillary is situated opposite the discharge 

 pore of a large sporangium, it is possible in the space of a few seconds to 



