i68 
Weston .— The Development of 
of Achtya polyandra, de Bary. This disagreement may possibly indicate that 
ciliate sporangiospores are developed only in some species of the genus, or 
that they are developed in the same species only under certain conditions. 
In any case, in view of the conditions in Thraustotheca , Aphanomyces , and 
Achtya , the assumption that automotility of the sporangiospores in the 
Saprolegniaceae is the prime factor in their escape may well be questioned. 
To a second theory, also, that the sporangiospores are forced out of the 
sporangium by the swelling of some gelatinous substance, no support 
is given by Thraustotheca. No such substance is demonstrated when 
spore liberation takes place in a suspension of India ink particles or in 
the presence of various stains. Moreover, in the other genera of the family 
this theory is not consistently supported. To be sure, de Bary ( 1 ), who 
first promulgated the theory for Achtyaprolifera, remained unshaken in his 
conviction throughout his long investigations, and Coker ( 7 ) corroborates 
him in the case of Achtya de Bary ana , Humph., while Rothert ( 25 ) main¬ 
tains that such an expulsive substance is present also in Aphanomyces 
laevis , de Bary. It must be noted, however, that de Bary and Rothert did 
not demonstrate this substance, but inferred its existence from the behaviour 
of the escaping spores; while Coker further maintained that the persistence 
of the spores in groups showed them to be still embedded in the substance 
which caused their expulsion, an interpretation which the normal adhesion 
of the spores by their viscid surfaces leads one to accept with reserve. 
Furthermore, Hartog ( 12 ) and Humphrey ( 15 ) were unable by seemingly 
conclusive tests to demonstrate such a substance in the case of Achtya ; 
while Rothert ( 24 ) offered somewhat less convincing evidence for Sapro- 
legnia. The expulsive material was generally supposed by Biisgen (6) and 
other investigators to be an intersporal substance derived from the gela- 
tinization of the ‘ cell plates * which they thought were formed between the 
spore initials. Walz ( 30 ), however, led by his observations on certain algae, 
maintained that gelatinization of the inner layers of the sporangium wall 
formed the expansive material which expelled the spores. In the case 
of Thraustotheca no evidence is found to support either of these views. 
A third theory was advanced in 1851 by A. Braun ( 5 ), who maintained 
that the contraction of the elastic sporangium wall, which had been distended 
by the swelling of the zoospores within, was instrumental in emptying the 
sporangium* With certain modifications this early theory seems applicable 
to the process of sporangium dehiscence and spore escape in Thraiistotheca. 
As has been said, the sporangiospores lack cilia, and no expulsive substance 
is apparent; but there is no doubt that the sporangiospores swell, and dis¬ 
tend the enveloping wall. It is obvious that even the slight increase in the 
size of the individual spores would, in large masses, produce a considerable 
aggregate increase in the sporangium volume and a proportionate distension 
of the wall. On the whole, the swelling of the sporangiospores against the 
