REMARKS ON THE PILOBOLIDAE 



187 



becomes cracked along these ridges and then the cracks appear 

 as Hnes which are whitish when contrasted with the dark sporangium- 

 wall. 



The formation of a jDattern on a discharged sporangium, con- 

 trary to the view expressed by van Tieghem, is not limited to 

 Pilobolus crystallinus, for I have observed patterns on the discharged 

 sporangia of P. Kleinii (Fig. 39, p. 83), P. longipes (Fig. 40, p. 84). 

 and P. umbonatus (Fig. 105, J, p. 210). 



While the existence of a pattern on a discharged and dried 

 sporangium cannot be held to be a diagnostic character for Pilobolus 

 crystallinus, yet differences in pattern are displayed by different 

 species. Thus a well-developed, discharged, and dried sporangium 

 exhibits : in P. Kleinii a few rounded regular dimples, one of which 



Fig. 94. — Pilobolus Kleinii. Diagram showing variations in tlie pattern on dried 

 discharged sporangia obtained ivom. a pure culture. A and B, sporangia with 

 a smooth wall. C-G, sporangia with one dimple, two, three, four, and five 

 dimples respectively. H, a sporangium with six dimples, one central. I, a 

 sporangium with six dimples in a circle. Magnification, 47. 



often holds a central position (Fig. 39) ; in P. longipes numerous 

 irregular somewhat gyrose depressions (Fig. 40) ; and in P. um- 

 bonatus, a central umbo with lateral more or less radial depressions 

 (Fig. 105, J). These differences in sporangial pattern are un- 

 doubtedly of diagnostic value and I have often used them in the 

 laboratory for distinguishing P. Kleinii, P. longipes and P. umbonatus 

 from one another. 



The pattern made by the dimples in the sporangial wall of dried 

 discharged sporangia of Pilobolus Kleinii varies considerably in 

 detail, as will appear in what follows. A pure culture of P. Kleinii 

 was obtained by inoculating sterilised horse dung with a single 

 sporangium. As soon as new sporangia began to be discharged, 

 they were caught on glass slides and examined under the microscope. 

 Whilst still wet, their sporangial walls were perfectly smooth ; but, 

 as they dried up, in the course of about two minutes, it was observed 

 that certain circular areas of the walls sank inwards and so formed 



