Johnson .- — Observations on Phaeozoosporeae. 141 
(1) that if the individual compartments in the chain are 
unilocular sporangia, each one will naturally have its own 
opening ; (2) that the form of the sporangiferous filament is 
such that it must have an unicellular origin ; (3) that in the 
formation of a plurilocular sporangium the division of the 
nucleus of the mother-cell takes place repeatedly, forming the 
rudiments of the zoospores, and that it is only after this that 
the cell-walls forming the compartments of the plurilocular 
sporangia are laid down. In A. villosa the mother-cell of 
the fertile filament divides, successively not simultaneously, 
into a number of cells, each of which becomes at once, in 
the chain, an independent cell with its own cell-wall ; each 
fertile cell then behaves like an unilocular sporangium, the 
nucleus divides repeatedly, and forms the rudiments of many 
zoospores in each chamber. Occasionally the apical cells 
of the filament are vegetative, making the fertile cells inter- 
calary. This is not merely a question of nomenclature, for 
the correct interpretation is of no small taxonomic import- 
ance. Broadly speaking, a plant with unilocular sporangia 
is of lower position, so far as reproduction is concerned, than 
one with plurilocular sporangia. Since the zoospores to 
which they give rise usually germinate independently, the 
unilocular sporangia may be regarded as asexual organs. 
Plurilocular sporangia, on the contrary, are known in several 
cases 1 to be gametangia , the contents showing a most in- 
teresting gradation in the differentiation of the sexual cells, 
tending towards the well-known mode of fertilisation in the 
Fucaceae. I do not overlook the possibility that the pluri- 
locular sporangia which have hitherto been described in 
A. villosa may occur, that I may not have had any plants 
bearing them, and that if I had I may have overlooked them. 
When my plants were examined as soon as possible after 
being dredged, they appeared to have monosporous com- 
partments : but on being kept in a darkened bottle for some 
hours, the multisporous condition revealed itself. 
1 Ectocarpus siliculosus , E. pusillus, Giraudia sphacelarioides. In Dictyosiphon 
hippuroides the unilocular zoosporangia are gametangia. 
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