276 DIVISION II,—COURSE OF DEVELOPMENT OF FUNGI. 
one another without interstices, the uppermost inclining towards one another and 
closing over the apex of the spore-chains ; and as this is done from the first, before 
the hymenial layer has reached its definitive breadth, the envelope is formed at least 
at the same time as the first basidia, and perhaps before them. All cells of the 
envelope are polyhedric in form, and are distinguished from the spores by their 
larger size, by their thicker wall which often shows a very delicate prismatic structure, 
and by their slightly granular or quite pellucid contents, ultimately often containing 
air. The spore-layer consisting of the spore-chains with the envelope increases in 
circumference by the constant introduction of new elements from the base and their 
subsequent enlargement, and encroaches on the surrounding pseudo-parenchyma. 
Its increase in breadth squeezes the adjacent cells together till they can often be 
no longer recognised. By its growth in length the summit of the perithecium 
is first pierced, the epidermis of the host is ruptured, and the spore-layer is 
raised with the summit of the perithecium above the epidermis and grows, if pro- 
tected from injury, by constant additions from below into a tube filled with spores 
and upwards of ı mm. in length. After it has burst through the epidermis, the 
cells of the envelope separate from one another 
at the apex, and the envelope itself opens out 
into the shape of a cup (Fig. 124 J a), or in 
4 some species (Gymnosporangium Sabinae) is 
9 split longitudinally into narrow lobes; the upper- 
most ripe spores fall out, and this disintegration 
of the envelope and the spore-chains advances 
in the direction of the base, more rapidly in 
exposed specimens and when the moisture of the 
surrounding atmosphere varies than in cultivated 
FIG. 126. Puccinta graminis. a median section and carefully protected plants. 
through a spermogonium in the leaf of Berberis vulga- 

ris, bursting out from the epidermis e—e. 6 sterig- . G ® 
mata from a similar spermogonium with young sper- The exceptional case mentioned above 1s 
Malia: @ Magn. 200? about 350 Ames, exemplified in the aecidia of the genus Phrag- 
midium, which are distinguished from all others 
in the mature state by having no compact tubular envelope. In place of an envelope 
a circle of club-shaped unicellular hairs, paraphyses, occupies the margin of the 
hymenia, which often spread out into broad cushion-like layers; their earlier de- 
velopment has not been investigated. 
Except in a very few cases the aecidia are always accompanied by sdermogonia, 
which are in all points very like the more simple organs of the same name described 
above in Collema and other Lichen-fungi (Figs. 124 I sp, 126). In most species they 
are small roundish to flask-shaped receptacles, looking to the naked eye like dots 
sunk in the subepidermal tissue, and have a thin smooth wall formed of several 
layers of closely woven hyphae which at length opens in the epidermis. The wall 
encloses a single cavity, and closely packed séerigmaéa springing from the whole of 
the inner surface of the cavity converge towards its centre leaving a narrow space free, 
which is afterwards densely filled with spermatia. A few rows of narrowly subulate 
pointed Zaraphyses or periphyses grow from the mouth of the receptacle instead of 
the sterigmata, and pierce through the epidermis and issue to the open air, forming 
a slightly divergent tuft, in the middle of which is the very narrow canal of the mouth, 
