i8o RESEARCHES ON FUNGI 



the older mycologists, are now at our disposal and would facilitate 

 the task. 



To the criteria so far employed by taxonomists for distinguishing 

 species of Pilobolus should be added : (1) the exact shape of the 

 subsporangial swelUng, whether elhpsoidal or pyriform, etc. ; (2) the 

 ratio of the width of the sporangium to the width of the sub- 

 sporangial swelhng ; (3) the nature of the depressions or wrinkles 

 on dried discharged sporangia when seen in strong reflected uni- 

 lateral light ; and (4) the nature of the fringe of the sporangium- 

 wall of dried discharged sporangia, in respect to form, colour, and 

 disposition of crystals. 



The spores of all the species of Pilobolus and Pilaira contain a 

 carotinoid pigment which colours oil-drops held within the proto- 

 plasm. Large spores which contain much of the pigment, e.g. those 

 of Pilobolus longipes and P. Kleinii, when seen singly in water in 

 transmitted hght, are orange-yellow, while small spores wliich 

 contain very little of the pigment, e.g. those of P. umbonatus, when 

 seen singly are almost colourless and when seen many together are 

 yellowish. 



Van Tieghem ^ remarked that the spores of Pilobolus longipes, 

 when seen in the mass, appear dull green, and he regarded this as 

 being due to the slaty-blue colour of the spore- wall combining with 

 the golden-yellow colour of the spore-protoplasm. When spores of 

 P. longipes are seen in the mass, they are seen by reflected and not 

 by transmitted light. I have observed that, if Pilobolus spores are 

 spread out in a drop of water under a cover-glass and are looked at 

 with the low-power objective of the microscope, they exhibit 

 dichroism, in that they are orange-j^ellow or yellowish in transmitted 

 light and green in reflected hght. This applies to the spores not 

 only of P. longipes, but also of P. Kleinii ^ and P. umbonatus. It is 

 therefore clear that a dull green colour for spores in the mass cannot 

 be regarded as a distinctive character of P. longipes. 



The basal swelling (trophocyst) of Pilobolus longipes, as com- 

 pared with that of other Piloboli, is so much elongated (Fig. 100, 



^ P. van Tieghem, " Troisieme memoire sur les Mucorinees," Ann. Sci. Nat., 

 6 ser., T. IV, 1876, p. 339. 

 2 Cf. supra, p. 72. 



