7- 



DIVISIOX 1. -GENERAL MORPHOLOGY. 



one belonging to the sixth youngesl spine in the chain. Phenomena essentially the 

 same occur in other species of the Uredineae, but with considerable variations in form 

 in the different species 1 . 



Where filiform sporophores rise free into the air, a further mechanical arrange- 

 ment is found which greatly assists the shedding and scattering of the abscised 

 spores. It ma) be readily observed in the Hyphomycetes s in Peronospora, for example, 

 Phytophthora infestans, and in the gonidiophores of Peziza Fuckeliana, &c. The 

 hyphae of these Fungi are cylindrical in the moist and turgescent state, but collapse 

 when dry and especially when the spores are ripe into a flat ribbon-like form 2 , 

 and the drier they are the more strongly do they become twisted round their own 

 longitudinal axis. They are so highly hygroscopic that the slightest change in the 

 humidity of the surrounding air, such for instance as may be caused by the breath 

 of the observer, at once produces changes in their turgescence and torsion ; the 



latter give a twirling motion to the extremity of the 

 gonidiophore and the ripe spores are thereby thrown 

 off in every direction. 



Abjection of acrogenous propagative cells is effected 

 by a mechanism which we shall have to speak of again in 

 section XXI. The cell which is to be abjected, whether 

 spore or spore-mother-cell (for brevity we shall call it 

 spore), is abjointed singly by a cross septum at the apex 

 of a tubular and often comparatively large sporiferous 

 cell, a basidium or a sterigma, which retains its parietal 

 protoplasm still intact after the abjunction of the spore 

 and is still turgescent in consequence of a continued 

 supply of water in increasing quantity. Its membrane 

 is highly extensible and elastic, and continues to stretch 

 as the tension increases with the increased amount of 

 water absorbed. But its cohesion is less over an annular 

 area immediately beneath the cross septum than in 

 any other part of the circumference, and if the tension reaches a certain point, 

 it overcomes the resistance of the less coherent annular zone, the suture of 

 dehiscence', the wall opens by a circular fissure, the pressure of turgescence is 

 instantly relieved and the elastic wall contracts, especially in the direction of die 

 verse diameter, and this causes a large part of the fluid contents to be squirted 

 out at the same moment with force through the fissure, and as it strikes full on the 

 transverse septum, the spore that rests upon the septum is abjected with it. The 

 basidium thus emptied collapses and perishes. 



The process of abjection may be observed most completely in the acrogenously 



abjointed spore-mother-cells of Pilobolus crystallinus and its nearest allies, of which 



hall speak again in later sections (Fig. 38). It occurs also, as Brefeld 3 has 



FIG. 38. Pilobolus Ccilif>its. 

 Diagrammatical r< n of a 



longitudinal section ; t upper end of 

 the sporiferous cell, s thi 

 will be abjected ; the tra 

 which forms i' I ielow thrusts 



llie interior of the 

 annular suture of 



it. Ztg. 1. c. p. 7S6. De B idpilze, p. 59. Reess, Rostpilzformen d. Coniferen, Halle, 



R. Hartig, Wichtige Krankh. d. Waldbaume, t. IV, V. 

 Fresenius, Beitr. t. II. 

 3 Bot. Ztg. 1870, p. 161. Abhandl. d. Naturf. Ges. zu Halle, Bd. XII, 1. 1871. 



