ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
491 
the unicellular sac of Caulerpa prolifera. He finds that the phenomenon 
bears no relation whatever to that of rotation in the higher plants, such 
as the familiar examples in Nitella and Hydrocharis , and but little to 
that of circulation such as is seen in the hairs of Tradescantia and 
Cucurbita. The parietal protoplasm of the mature “ leaves ” contains an 
uninterrupted layer of chlorophyll-grains, in which no motion whatever 
could be detected. The motion is observed mainly in the strings of 
protoplasm which pass from one to another of the beams of cellulose 
which occur in such large numbers in the interior of the cell ; these 
strings form a continuous mass of protoplasm with the protoplasmic 
layers which invest the cellulose-beams. The beams increase in number 
from the base towards the apex of the “leaf.” The protoplasmic strings 
inclose chlorophyll-grains which are carried along in the current. 
Branches of these strings run into the prolitications. 
No similar movement of the protoplasm, or only a very feeble one, 
was observed in Valonia , Bryopsis, or Codium ; in Acetabularia mediter- 
ranea it was much more apparent. 
Injury to the leaves of Caulerpa is speedily remedied, first by 
accumulation of the protoplasm which escapes from the wound, followed 
by copious formation of cellulose. The protoplasmic phenomena in the 
rhizome and in the rhizoid correspond, in general terms, with those in 
the leaf. 
The familiar beams of cellulose are outgrowths from the inner side 
of the cell-wall. Their main function appears to be to preserve the form 
of the organ in which they are found under different degrees of turgidity ; 
if they are cut through, the leaf increases very greatly in thickness. 
They also aid, through their protoplasmic envelope, in guiding the 
currents of protoplasm within the cell which serve for the transport of 
the food-materials. 
Fungi. 
Nucleus of Peronospora.* — Mr. H. W. T. Wager has investigated 
the structure of the nuclei in Peronospora parasitica , a common parasite 
on cruciferous plants, and their behaviour during the formation of the 
oosperm. The following is a summary of the results. 
Mycele, antherids, oogones, and gonids (spores) contain numerous 
deeply-staining nuclei which exhibit a very clear nuclear structure. 
The division of the nucleus takes place by a process of karyokinesis 
similar to that which occurs in the higher plants. This can be most 
satisfactorily observed in the nuclei of the oogone. These are, at an 
early stage, spherical or slightly oval vesicular bodies, each of which 
contains a large mass of chromatin, forming a peripheral layer on its 
wall. All the nuclei of the oogone divide, and the process of division is 
accompanied by complicated changes in the protoplasm, leading to the 
formation of the oosphere. At an early stage the protoplasm of the 
oogone appears to be a homogeneous granular mass, containing numerous 
nuclei. A number of vacuoles appeal’ in the centre of the oogone, 
and cause the greater part of the protoplasm to be restricted to the 
* Ann. of Bot., iv. (1890) pp. 127-46 (1 pi.). 
2 M 2 
