502 NOTICES OF BOOKS. 
of interest, both on account of the remarkable manner in which 
it takes place, and because it unfolds, as I believe, the nature of 
the process in other families, and furnishes a valuable addition to 
our knowledge of their structure and physiology. The compressed 
and deeply restricted cells of Huastrum offer most favorable oppor- 
tunities for ascertaining the manner of the division; for although 
the frond is really a single cell, yet this cell in all its stages ap- 
pears like two, the segments being always distinct, even from the 
commencement. As the connecting portion is so small, and neces- 
sarily produces the new segments, which cannot arise from a 
broader base than its opening, these are at first very minute, 
though they rapidly increase in size. The segments are separated 
by the elongation of the connecting tube, which is converted into 
two roundish hyaline lobules. These lobules increase in size, 
acquire colour, and gradually put on the appearance of the old 
portions. Of course, as they increase, the original segments are 
pushed further asunder, and at length are disconnected, each 
taking with it a new segment to supply the place of that from 
which it had separated. It is curious to trace the progress in de- 
velopment of the new portions. At first they are devoid of colour, 
and have much the appearance of condensed gelatine, but as they 
increase in size the internal fluid acquires a green tint, which is at 
first very faint, but soon becomes darker; at length it assumes a 
granular state. At the same time the new segments increase in 
size and obtain their normal figure; the covering in some species 
shows the presence of puncta or granules; and lastly, in Xanthi- 
dium and Staurastrum the spines and processes make their appear- 
ance, beginning as new tubercles, and then lengthening until they 
attain their perfect form and size; but complete separation fre- 
quently occurs before the whole process is completed. This sin- 
gular process is repeatede again and again, so that the older 
segments are united successively, as it were, with many gene- 
rations.” 
The mode of reproduction in these minute plants, seeming as it 
does to throw much light upon the same process in the higher 
tribes of plants, is another part of the subject of especial interest 
