14 RESEARCHES ON FUNGI 



The Cytology of Pilobolus. — Harper ^ in 1899, as the result of an 

 investigation made with modern technical methods, gave an account 

 of the cytological changes which take place during the formation 

 of the sporangiophore and sporangium of Pilobolus crystallinus, 

 P. oedipus, and P. microsporus. His observations were as follows. 



In seven to eight days after the spores have been sown on steri- 

 Used horse dung, the sporangiophores begin to appear. The yellow 

 bulb-like swelUng of the mycehum, from which a sporangiophore 

 arises, appears in the afternoon and at that time the vegetative 

 nuclei within it divide rapidly. After these divisions have been 

 completed, the sporangiophore grows out from the swelHng and most 

 of the cytoplasm flows upwards into the sporangiophore carrying 

 nuclei with it. The end of the sporangiophore swells up to form 

 the sporangium, and cytoplasm and nuclei pass upwards into it 

 (Fig. 7, A-C). The protoplasm in the sporangium at first forms a 

 spongy framework in whose meshes is a considerable amount of 

 cell-sap ; but, later, it becomes truly vacuolated in that it comes to 

 contain rounded cavities whose outUnes are determined by surface 

 tension. A layer of larger flattened vacuoles comes to lie in the 

 curved surface which marks the outUne of the future columefla 

 (Fig. 7, D, v). Then protoplasmic cleavage starts from the edge 

 of the sporangiophore and pushes upwards (Fig. 7, D, c c) ; and 

 this cleavage, aided by the fusion of certain of the flattened vacuoles, 

 results in the formation of a dome-shaped furrow (Fig. 7, E, c) 

 which separates the sporangium from the sporangiophore. The 

 cell- wall is then deposited in the cleft between the two membranes. 



A jelly-hke substance is excreted by the spore-plasma and is 

 deposited as a layer on the inside of the lower part of the wall of the 

 sporangium, and there is an extension of it up the wall of the 

 columella (Fig. 7, E, b, and H, a, and Fig. 8, D, d). The sub- 

 sporangial swelling begins to be formed beneath the sporangium late 

 in the afternoon. When full-grown its wall is Hned by a thin layer 

 of protoplasm containing many nuclei. 



Cleavage of the spore-plasma begins shortly after the columella is 

 complete (Fig. 7, E). The protoplasm becomes somewhat vacuolar and 

 the nuclei are rather evenly distributed through its mass. Cleavage 



1 R. A. Harper, "Cell-Division in Sporangia and Asci," Annals of Botany, 

 Vol. XIII, 1899, pp. 490-503, Plates XXIV-XXVI. 



