MOVEMENTS OF PROTOPLASM IN CELL-CAVITIES. 33 
at rest at any time, except perhaps during periods of drought in summer and of 
frost in winter, and in seeds during their time of quiescence. This applies par- 
ticularly to immature cells. In them the protoplast forms a solid body whose 
substance entirely fills the cell-cavity. The young cell, however, grows up quickly, 
its cavity is enlarged, and the space, hitherto filled by the protoplast, becomes two 
or three times as large as before. But the increase of volume on the part of the 
protoplast itself does not keep pace with the enlargement of its habitation. It is 
true that it continues to cling closely to the inner face of the cell-wall, thus forming 
the primordial utricle; but the more central part of its body relaxes, and in it are 
formed vacant spaces, the vacuoles above mentioned, wherein collects a watery 
fluid known as the “cell-sap.” The portions of protoplasm which lie between 
the vacuoles resolve themselves gradually into thin partitions bounding them; and 
lastly, these partitions split up into bands, bridles, and threads, which stretch across 
the cell-cavity from one side of the primordial utricle to the other, and are woven 
together here and there where they intersect. With these protoplasmic strands we 
have already become acquainted. 
But the protoplasm in the interior of a growing cell, whilst relaxing and 
breaking up, also becomes motile if the liquid attaıns a certain temperature, and 
then the appearance presented is like that of a lump of wax melting under the 
action of heat. These movements may be observed very clearly under the miero- 
scope in the case of large cells with thin and very transparent cell-membranes, 
especially when the colourless, translucent, and gelatinous substance of the proto- 
plasm—not always sharply defined in eontour—happens to be studded with 
minute dark granules, the so-called “microsomata.” These granules are driven 
backwards and forwards with the stream, like particles of mud in turbid water, and 
their motion reveals that of the protoplasm wherein they are embedded. Seeing 
particles gliding in all directions through the cell-cavity, arranged irregularly in 
chains, rows, and clusters in the protoplasmic strands, we are justified in concluding 
that this motion takes place in the substance of the strands itself. 'The movement, 
moreover, is not confined to isolated strands, but occurs in all. Granular currents 
flow hither and thither, now uniting, now again dividing. They often run in 
opposite directions even when only a trifling distance apart; sometimes two chains 
are drifted in this way when actually close together in the same band of proto- 
plasm. The streams pour along the primordial utricle and whilst there divide into 
a number of arms, meeting and stemming one another and forming little eddies; 
then they are gathered together again and turn into another strand of the more 
central protoplasm. The individual granules in the currents are seen to move with 
unequal rapidity according to their sizes; the smaller particles progress faster than 
the larger, and the larger are often overtaken by the less, and when this happens 
the result often is that the entire stream stops. If so, however, the crowded 
particles are suddenly rolled forward again at a swifter pace, like bits of stone in 
the bed of a river as it passes from a level valley into a gorge. The course of the 
SPSS protoplasm remains throughout sharply marked off from the watery sap 
Vou. I. 3 
