MOVEMENTS DUE TO TURGOR AND GROWTH 



423 



ment a circular patch at the apex of the ascus can no longer withstand the 



pressure inside, and it forthwith bursts. In consequence of the pressure 



of the elastic and contractile membrane the entire contents of the cells are 



at once ejected through the opening, in the case of Ascobolus to a height of 



seven or more cm., and in Sordaria fimiseda to as much as 15 cm., whfld the 



wall at once contracts to its original dimensions. In Ascobolus a large number 



of asci burst at the same moment in the day, i. e. between one and three o'clock, 



the extension and extrusion from the hymenial surface having begun the 



evening before. The ejection occurs then after a very gentle 



shaking, which probably acts so as to cause a slight bending 



of the ascus and in this way an increased stretching of the 



membrane beyond the capacity of the apical region to with- 



stand ; at the same time it can scarcely be doubted that in 



the long run ejection may occur without such oscillation. 



This daily periodicity in the ejection of spores is obviously 



dependent on light, but into these relationships we cannot 



enter here. Nor can we discuss in detail the various 



means whereby asci open, for the isolation of an apical lid 



as in Ascobolus is by no means general. 



A certain amount of interest, however, attaches to the 

 type of ascus which ejects its spores one at a time, as 

 takes place in many Pyrenomycetes, e.g. Sphaeria scirpi 

 (PRINGSHEIM, 1858). Before the spores begin to be ejected 

 a sudden extension of the ascus takes place, amounting to as 

 much as three times its original length. As a consequence, 

 the outer lamella of the wall of the ascus is ruptured, and rolls up, while the 

 inner lamella becomes stretched (Fig. 127) ; a tension thus arises between two 

 layers of the cell- wall not previously exhibiting any difference. By the vigorous 

 extension of the ascus the spores (which are in this case multicellular), are 

 pushed towards the apex, and very soon the uppermost spore is ejected through 

 the apical opening. As the ascus contracts it becomes slightly shorter and the 

 next spore at the same time closes the aperture, and so renders any further exit 

 of cell contents impossible. Thereupon ensues a fresh increase in osmotic ten- 

 sion in the ascus, increasing until the second spore is 

 ejected through the narrow aperture, and so on. When 

 all the spores are shed the ascus contracts markedly, and 

 at the same time its wall becomes much swollen, and 

 hence it is very apparent that the ejection is not occa- 

 sioned by osmotic pressure, or at least not by that only, 

 but that swelling of the cell-membrane, may take part 

 in the process. Similarly in many other lower organisms 

 the spores are pressed out of the mother-cell by swelling 

 of certain parts of the cell- wall. 



Osmotic activity is, however, responsible for the 

 ejection of the spores of Empusa and its allies (e.g. 

 Basidiobolus, p. 249) and for the corresponding pheno- 

 menon in the sporangia of Pilobolus. Let us consider the 



of Pilobolus crystallinus (compare DE BARY, 1884). 



empty ascus. x 150. 

 After DE BARY (Morph. 

 d. Pilze. Leipzig, 1884). 



Fig. is?. Sphaeria s 

 7, extended ascus, the outer 

 layer of the wall burst. 77, 

 the last spore has not as yet 

 been extruded. 777, empty 

 ascus. After PFEFFER (Pflan- 

 zenphysiologie, ist edition). 



case 



In this plant we have a sporangiophore (/, in Fig. 128) 



which is much swollen and whose termination is inserted 



into the base of the sporangium. When the pressure in the sporangiophore 



has reached a certain height a circular rupture occurs in the membrane at r and 



the contents of the cell are, owing to the contraction of the wall, ejected just as 



in the case of the ascus of Ascobolus. The liquid which is ejected from the 



sporangium in this case may be thrown into the air to a height of a metre. 



