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The objects for exhibition under the twenty-four microscopes 
now installed have been selected from among the lower plants. 
Changes in the objects have been made from time to time, 
with the aim of increasing the attractiveness and the instructive 
qualities of the display. The objects on exhibition at the pres- 
ent time, with the explanatory labels, are as follows: 
1. PLASMODIUM OF A SuimME MouLp (Physarum cinereum). 
The slime moulds (Myxomycetes) are among the most simple 
of organisms. They form coatings on bark, leaves and dead 
wood in shaded or damp places. They have two stages of exist- 
ence, (1) the vegetative stage or plasmodium, composed of naked 
protoplasm ; (2) the spore-bearing stage, in which small struc- 
tures filled with propagating bodies (spores) are formed from the 
protoplasm. In the vegetative state, here represented, the organ- 
ism is strikingly similar in its essential attributes to some of the 
lower animals. 
2. SPORE-BEARING STAGE OF A SLIME MouLp (Dictydium umbil- 
calum 
This slime mould, like many of its relatives, grows upon decay- 
ing wood. e stalks and the netted framework of the spore- 
case walls remain, but the spores have mostly fallen. A few of 
the spores, however, appearing like minute, dark dots under the 
present magnification, can be detected, adhering to the network. 
3. A Diatom (/sthimia nervosa). 
The diatoms are minute one-celled plants. The living matter 
of each is enclosed and protected by a hard, though thin and 
transparent, siliceous wall. This consists of two separable parts, 
one of which fits ¢nside the other like a bandbox and its cover. 
In this specimen the organic matter has been removed by the use 
of acids, leaving only the siliceous walls, which are marked with 
pits, ridges and furrows. Some kinds of diatoms have the power 
of free animal-like locomotion. 
4. A GREEN FRESH-wWATER AGA (Draparnaldia). 
A fresh-water relative of the seaweeds. It occurs in clear pools 
and in slow-flowing streams. This specimen shows the vegeta- 
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