580 Acton. — Botrydina vulgaris , Brdbisson , 
De Toni (’ 89) 1 did not consider the plant as an alga, and only refers 
to it as c Sistit Hepaticarum propagula \ 
West (’ 04 ) 2 states that the genus requires further investigation. 
The specimens of Botrydina examined were growing indiscriminately 
amongst a Moss and an Hepatic, covering the shoots with a layer of dark 
green globular structures just visible to the naked eye. So freely was it 
growing that it was often difficult to distinguish the individual leaves of the 
Bryophyte. The Botrydina was firmly attached in some way to the shoots, 
and appeared to bind the leaves together by its growth (see PI. XLIV, 
Fig. 1). 
A microscopic examination showed the dark green bodies (varying in 
diameter from 20 to 300 \x) embedded in mucilage, by which they were 
attached to the shoots. The mucilage was traversed by fungal hyphae. 
Each globular structure consisted of a central mass of green cells invested 
by a colourless envelope of considerable thickness, which was apparently 
cellular. This was present in all cases, and showed little variation in 
thickness, being almost as thick in the smallest specimens as in the largest 
ones. The smaller specimens were subspherical, but the older ones showed 
a tendency to become irregular in shape as they increased in size, and in 
some cases two or three had become confluent, forming an irregular mass 
about 500 fA in diameter. 
Cultures. 
The apparent cellular structure of the colourless envelope formed 
a striking feature of the plant, and, with a view to ascertaining how this was 
formed, cultures of Botrydina were started early in July, 1908. The cultures 
were made in Petri dishes containing peptonized agar, and in culture dishes 
containing Knop’s solution of various strengths. These were all overgrown 
by moulds and bacteria, and at the end of July a fresh series of cultures 
was made, taking every possible precaution to obtain them pure. 
Hanging-drop cultures were made in water and Knop’s solution. In 
the majority of these the Botrydina turned brown and died in a few days, 
evidently killed by the active development of fungal hyphae. In other 
cases the cover-glass soon swarmed with a small unicellular green alga, the 
active growth of this preventing the development of Botrydina. 
Two cultures were made in 0*25 per cent. Knop’s solution. In both 
cases there was at first a slight development of a fungus, but this soon 
ceased and a green alga appeared. One culture consisted mainly of 
Stichococcus Jlaccidus , a subaerial alga which was evidently present among 
the original tufts of moss ; but the other, after a period of fourteen days, 
was practically a pure culture of the unicellular green alga which had 
1 De Toni, Sylloge Algarum, 1889, vol. i, p. 667. 
2 G. S. West, Treatise Brit. Freshw. Alg., Cambridge, 1904, p. 247. 
