72 DIVISION I.-—GENERAL MORPHOLOGY. 
one belonging to the sixth youngest spore in the chain. Phenomena essentially the 
same occur in other species of the Uredineae, but with considerable variations in form 
in the different species. 
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 may be readily observed in the Hyphomycetes, 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’, 
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 
pie Be Pieteen cota. Mane supply of water in increasing quantity. Its membrane 
ogi Pf uectea ed is highly extensible and elastic, and continues to stretch 
ee ei “AS the tension increases with the increased amount of 
ir Ile tie Meer of the: 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 the 
transverse 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. 2 
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 
we shall speak again in later sections (Fig. 38). It occurs also, as Brefeld® has 



1 Bot. Ztg. 1. c. p. 786. De Bary, Brandpilze, p. 59. Reess, Rostpilzformen d. Coniferen, Halle, 
1869. R. Hartig, Wichtige Krankh. d. Waldbäume, t. IV, V. 
2 Fresenius, Beitr. t. II. 
® Bot. Ztg. 1870, p. 161. Abhandl. d. Naturf. Ges. zu Halle, Bd. XII, 1. 1871. 
