164 
Weston.—The Development of 
which eventually forms a mycelium. In the case of sporangiospores retained 
in unemptied or partially emptied sporangia, the germ-tubes make their way 
through the enveloping sporangial wall (Fig. 31), a condition presenting 
close resemblance to the doubtful genus Aplanes. 
The development of dwarf sporangia from the sporangiospores is shown 
in Figs. 26, 28,32, 33, and 34. Within these dwarf sporangia are formed 
two or three spores somewhat smaller than the normal. Since the total 
expansion of so few spores is insufficient to rupture the sporangium wall, the 
spores remain in situ , and emit their zoospores through the enveloping 
membrane (Figs. 26 and 34). These zoospores differ from those already 
described only in their smaller size and shorter motile period. This 
phenomenon of dwarf sporangium formation presents an interesting analogy 
to the production of secondary conidia in the case of certain Entomo- 
phthoreae and Peronosporaceae. 
Gemmae. In Thraustotheca gemmae are formed when environmental 
conditions inhibit the development of reproductive organs but permit 
vegetative growth. By maintaining vigorous mycelia at a temperature 
(31-32 0 C.) near the maximum, or in harmless salt solutions at concentrations 
suppressing the formation of other organs, the formation of gemmae is easily 
induced. Under these conditionss porangium and oogonium initials, as well 
as portions of the hyphae, are walled off and become inactive. The gemmae 
thus formed may be clavate (PI. V, Fig. 42), spherical (Figs. 43, 46, and 
48), cylindrical, or irregular (Fig. 47) in form, and show variations in density 
of content and thickness of wall. They cannot survive desiccation ; and 
since their metabolic activity, though diminished, still continues, their 
endurance is proportionate to the amount of protoplasm they contain. 
When inhibitory conditions are removed, the gemmae resume their 
growth and give rise to vegetative hyphae (Fig. 48), sporangia (Figs. 42 and 
43), secondary gemmae (Figs. 45 and 46), or sexual organs. In this connexion 
the initial tendency of the structure from which the gemmae arose has 
no influence ; since any gemma may produce any type of vegetative or 
reproductive structure—the process being governed by the same rules which 
apply in the development of these structures from the mycelium. 
In view of the conditions under which the gemmae arise, and_of the lack 
of physiological and morphological fixity which characterizes them, Mauri- 
zio’s (20) opinion that they should be regarded as phylogenetically significant 
seems hardly justifiable. On the contrary, in the present instance, as in the 
case of Saprolegnia mixta (cf. Klebs, 18 ), they appear to be ‘ Hemmungs- 
bildungen ’ representing only a transient resting-state induced b}' unfavour¬ 
able conditions. 
The sexual reproduction of Thraustotheca closely resembles that of the 
prolifer a group of the genus Achlya. 
Antheridia. The antheridial filaments arise at intervals along the 
