4 MR. W. PHILLIPS ON THE GENUS VIBRISSEA. 
itself into a bundle of eight straight slender transparent threads, occupying the whole 
interior of the mother cell—the ascus. А perfect ascus measures "25 millim. long and 
:005 millim. broad. | 
The sporidia, when mature, are long slender filiform bodies, tapering at the extremities, 
the protoplasm they contain being at first arranged in irregularly-sized globules, but 
ultimately, expanding, give the appearance of cells divided by walls at nearly equal 
intervals throughout their entire length. Іп comparison with those of other Discomycetes, 
the sporidia are very long. 
The paraphyses which form the greater part of the hymenial layer are long slender 
filaments rising above the asci, having enlarged club-shaped apices filled with the colour- 
ing-matter that gives the characteristic colour to the hymenium. They are once, twice, 
or thrice branched from near the top, and are divided by septa at remote intervals. 
Having given a brief description of the structure of the several parts of Vibrissea 
truncorum, it is necessary to offer an explanation of the phenomenon which was the 
main ground with Fries for establishing the genus—namely the violent ejection of the 
sporidia when subjected to a change in the hygrometrical state of the atmosphere, and 
the consequent velvety appearance assumed by the hymenium, owing to many of the 
sporidia remaining attached by their lower extremities to the surface of the hymenium. 
It is a well-known fact that the habit of shooting forth the sporidia from the asci with 
considerable force is more or less common throughout the whole of the Discomycetes ; 
while in the genus Ascobolus the asci themselves become separated from the subhymenial 
tissue, and are forced upwards above the general level of the hymenium. The mutual 
pressure produced in a bed of closely set paraphyses and asci, the whole possessing a 
great capacity for the absorption of moisture, by which the entire mass is made to occupy 
а space exceeding the capacity of the receptacle, will account in Peziza for the more 
mature asci (the walls of which have become thin by expansion) bursting at the point of 
least resistance, which is the summit, thus allowing their contents to be ejected. In the 
genus Vibrissea, however, this mode of accounting for the ejection of the sporidia will 
not apply; for the phenomenon does not take place on expansion of the hymenium by 
absorption of moisture, but on contraction produced by drying. "The normal condition 
of the hymenium of Vibrissea is complete saturation, owing to the plants growing in 
water; and the shooting forth of the sporidia is not witnessed till they are taken out of 
the water and exposed to the atmosphere. We are compelled, therefore, to seek some 
other explanation. I submit the following. 
The greatly distended hymenium in a mature plant assumes a highly convex form, 
being forced considerably above the margin of the receptacle, in many cases bending 
over the margin, so as to become concave ‘beneath, the subhymenial tissue necessarily 
taking a convex form, while the meduilary tissue of the stem is extended lengthwise to 
its utmost eapacity. "The cortical tissue is less affected by moisture and more rigid in 
texture. This being the condition of things when a plant is removed from water and 
exposed to the drying influence of the atmosphere, evaporation at once takes place, when 
the medullary tissue contracts in length, draws down the subhymenial tissue, together 
with the hymenium, into the already too narrow receptacle, thus causing violent lateral 
