120 THE AUSTRALIAN NATURALIST. 
This water is charged with various salts necessary for 
the nutrition of the plant, and these dissolved salts are 
carried into the cell at the same time as the water enters. 
Thus the same cell wall which is impervious to the sap 
is permeable to the smaller molecules of the soluble salts. 
A partial explanation of this important difference from 
the perfect physical membrane is afforded by a considera- 
tion of the coarse-grainedness of the protoplasm, which 
forms the outer wall of the cell. If this cell-wall is con- 
stituted with a coarse enough mesh, it will allow water 
and the molecules of soluble salts to pass through, whilst 
stopping the passage of the larger molecules contained in 
the sap. 
Several cases in which this simple mechanical ex- 
planation is inadequate were pointed out, and some pos- 
sible explanations discussed. 
Some further experiments were shown of the growth - 
of colloidal membranes of various silicates, which are 
readily formed by putting small crystals of various metallic 
salts in a dilute solution of water-glass. 
ENCOUNTER BETWEEN SAND WASP (BXEIRUS 
LATERITUS) AND BURROW SPIDER 
(LYCOS GODEFFROYI). 
By Miss G. F. Froaaarr. 
We were at lunch when we saw the fight begin on 
the grass plot just in front of the window. We reached 
there in time to see the yellow and black fury hurl her- 
self at the big brown spider, many of which have silk- 
lined burrows in the turf. The spider was three times 
as big as the sandwasp, but was bewildered by the savage 
onslaught, and unable to parry the darting sting with 
which the wasp kept pricking it, always managing to 
pierce it underneath the body. In a minute or two, how- 
ever, the spider suddenly leapt up and sprang away 
frenziedly the wasp searched about, tripping among the 
grasses and using her wings to find where the spider had 
jumped. as 
That was the spider’s last bid for freedom. Fiercely 
the wasp flung herself at it again, stinging it on the under- 
side of its head, when it stopped all movement, 
