152 DIVISION II.—COURSE OF DEVELOPMENT OF FUNGI. 
basal transverse wall ; their wall, except at the plane of insertion and the parts imme- 
diately adjoining, deliquesce in water when it is mature. In the other genera (Fig. 71) 
the basal wall of all or of the larger sporangia expands into a conical dome-like or 
ellipsoid form and projects into the cavity of the spotangium, and from its shape is 
termed the columella. Among these genera is Pilobolus: its sporangium thick-walled 
with a basal expanding layer (p. 83), solitary terminal on an unbranched turgescent 
vesicular sporangiophore, from which it is abjected when ripe or (Pilaira, V. Tieghem) re- 
moved by swelling.—Mucor : outer wall of sporangium deliquescing when mature, usually 
incrusted on the outside with short spreading needles of calcium oxalate ; sporangio- 
phore narrow filiform, with or without single branches arising monopodially (Phy- 
comyces, Spinellus = Mucor fusiger but differing from Mucor in the formation of the 
zygospores, Sporodinia differing in its dichotomous sporangiophores and suspensors). 
The sporangia in the genera Rhizopus, Circinella, and Absidia have the same 
structure as in Mucor, but the filiform sporangiophores branch sympodially. In 
Rhizopus and especially Rh. nigricans (= Mucor stolonifer) the sporangiophores rise 
like stolons from the mycelium, ascending at first in a curve and then letting their 
points drop downwards. In this way they may reach a length of from one to several 
centimetres. If their apex touches a firm substratum, the previous growth in length 
ceases, and a number of incipient branches make their appearance behind the 
apex. Some of these branches develope with the apex of the stolon itself into shortly- 
branched rhizoids closely appressed to the substratum; others, usually from three 
to five in number, raise themselves above the substratum and become rigid branchlets 
2-3 mm. in height, each of which terminates in a sporangium ; lastly, one or a few 
of them develope as stolons which may repeat the same course of development’. 
Absidia has according to Van Tieghem a similar mode of growth to Rhizopus, but 
with the difference that the stolons of the successive orders describe very regular 
curves, and that a tuft of sporangiferous branches spring above from the convexity 
of the curve. On the erect sympodial sporangiophores of Circinella see Van Tieghem, 
as cited in end of section XLIV. While the above genera have sporangia of only one 
kind, those which constitute the Thamnidium group have two kinds: large ones 
quite like those of Mucor, and terminal like them on the primary stem of the sporan- 
giophore which is monopodially branched or not branched at all; and small ones, 
sporangiola, usually formed on the extremities of the many ramifications of lateral 
branches of the sporangiophore which ends itself in a large sporangium. In all the 
species of this group sporangiophores occur which only produce one large sporan- 
gium, and others which produce only sporangiola. The sporangiola are distinguished 
from the sporangia not only by their small size and the reduction of the number of 
their spores to 2 or 1, but also by their level or slightly convex basal wall, which does 
not rise high into a columella, and the comparatively thick smooth outer wall without 
incrustations, which persists till after the ripening of the spores and is in many cases 
only burst by their germination. There is no difference in the germination of the two 
kinds of spores or in their products. Van Tieghem distinguishes the genera Thamni- 
dium, Chaetostylum, and Helicostylum by the shape and ramification of the branch- 
lets that bear the sporangiola. 
2. CHAETOCLADIEAE. The genus Chaetocladium which forms this division 
contains two species very like one another, which are usually parasitic on the larger 
Mucoreae in the manner described in section V. The filiform erect gonidiophores 
produced from the zygospore usually terminate in a slender subulate hair-point, 
beneath which they form a whorl of usually 2-5 short branches standing out at a 
right angle, which again branch and form further whorls of a second or third order. 
The branching axes which become shorter with each successive order end each in its 

1 On deviations from this rule of growth see de Bary, Beitr. II, and Wortmann in Bot. Ztg. 
1881, p. 368, 
