142 



RESEARCHES ON FUNGI 



osmotic pressure increase in length while those with the lower 

 osmotic pressure decrease in length. 



In accordance with the details of Barger's technique : the 

 capillary tubes were made about 6-8 cm. long and with a bore about 

 1-0 mm. in diameter ; seven alternating drops separated by short 

 air-spaces were introduced into each capillary tube (Fig. 68) ; the 

 ends of the filled tubes were sealed up in a flame ; two or three tubes 

 with like contents were attached with Canada balsam to a glass 

 slide ; the slide was immersed in water at room temperature, the 

 water being contained in a Petri dish ; the lengths of the five central 



Fig. 69. — Optical section tlirougli part of a capillary tube used for determining 

 the osmotic pressure of the cell-sap of Pilobolus longipes by the Barger 

 method, showing the appearance of a drop when its length is being 

 measured with the scale of the eye-piece inicrometer of the microscope. 

 The length of the drop here shown is 28*2 units of the scale. Magnifi- 

 cation, 27. 



shorter drops (two of the standard solution, sucrose, and three of the 

 ceU-sap of Pilobolus) were measured (Fig. 69) under the microscope 

 with the help of an eye-piece micrometer shortly after the tubes had 

 been placed in the water ; and the drops were measured again next 

 day after a lapse of 30-36 hours. 



The sap was obtained as follows. Fresh dung from a stable was 

 spread out on the floor of a large glass case. On the fourth day 

 thereafter, many thousands of fruit-bodies of Pilobolus longix>es 

 (Fig. 70) came to maturity without any admixture of Mucor, etc. 

 When the fruit-bodies were beginning to discharge their sporangia, 

 they were caused to burst by pressing their subsporangial swellings 

 (c/. Fig. 18, p. 50) against a glass slide. As soon as the sap thereby 

 set free amounted to about two drops, it was allowed to run off the 

 slide into a test-tube. When a sufficient quantity of the sap had 



