170 Weston.—The Development of 
presents several striking points of similarity. In each case the sporangium 
consists of an enveloping membrane surrounding a number of discrete 
spores. Papillae of dehiscence, also, may be induced in Thranstotheca ; 
and in Achtya , although they are of normal occurrence, may vary greatly, 
and even become non-functional. Moreover, although the escaping 
sporangiospores of Thranstotheca do not form the hollow sphere charac¬ 
teristic of most species of Achtya , they show a degree of adelphotaxy at 
least comparable to that characterizing A. paradoxa, Coker. Furthermore, 
the sexual organs of Thranstotheca very closely resemble those of the 
prolifera group of the genus Achtya. These resemblances do not, of course, 
prove any relationship ; but they do seem sufficient to entitle Thranstotheca 
to a tentative systematic position near Achtya rather than Dictynchns. 
Summary. 
1. In the processes of sporangium formation and spore liberation 
Thranstotheca agrees with other members of the family. The intersporal 
substance mentioned by early investigators cannot be demonstrated. 
2. Thranstotheca is unique among the Saprolegniaceae in that the 
non-motile sporangiospores escape by bursting the sporangium wall. The 
fragility of the sporangium wall has been greatly over-emphasized. 
3. The sporangiospores may emit motile zoospores, give rise to 
hyphae of germination, or form dwarf sporangia, according to conditions of 
the environment. 
4. The zoospores are grooved, laterally biciliate, and of a characteristic 
shape that cannot be adequately described by the terms ‘ reniform ’ or 
‘ bean-shaped ’, that are generally used in this connexion. 
5. Gemmae are formed, but represent merely a transient resting state 
induced by unfavourable environmental conditions. 
6. In the development of the sexual structures certain phenomena 
seem to justify the assumption that the formation of antheridia is dependent 
on contact of the antheridial filaments with the oogonia; and that oospore 
formation is, under normal circumstances, definitely correlated with the 
presence of antheridia on the oogonia. 
7. In germination the oospores send out hyphae which either, after 
limited growth, form sporangia or give rise to extensive mycelia—the type 
of development depending on the amount of nutriment available. 
8. In its structure and development Thranstotheca shows a resemblance 
to Achtya that, in the opinion of the writer, is sufficient to entitle it to 
a systematic position near the latter genus rather than near Dictynchns. 
