426 
POPULAR SCIENCE REVIEW. 
has been pointed out by Mr. Thomas Meehan. The vertical section showed 
by the annual rings of wood that it was about twelve years old. After the 
eighth year’s circle there was a layer of bark, and over this layer two more 
circles of wood. On a portion of the section another layer of bark had 
formed between the tenth and eleventh years’ circles of wood. The bark 
seemed to be wholly of liber, tlie cellular matter and external cortical-layer 
of the regular bark appeared to be wanting. A longitudinal section showed 
where these internal layers of bark extended no further upwards, and at 
this point there was an evident show of wood from the interior over and 
down this layer of inclosed bark. He remarked that this section of wood 
was taken from a stem which had been led to support itself in an upright 
position. When the Wistaria is permitted to trail along the ground, 
numerous rootlets are formed along its length. He thought, from the ap- 
pearance of the wood in the specimen presented, that rootlets had partially 
formed in these erect stems, pushing through the liber; and then, instead of 
penetrating entirely through the bark, and forming perfect rootlets, they 
remained within the cellular matter, and descending joined with the regular 
woody layer in forming an annular course of wood. This explanation was 
the more plausible, he thought, from the fact that woody stems formed on 
the ground. Where the rootlets went quite through into the earth, the 
stems were nearly regularly cylindrical ; but these upright steins, on which 
rootlets were never seen, had an irregular fluted appearance ; of course, this 
explanation does not accord with the formation of wood in ligneous struc- 
tures as generally understood ; but he could not understand how the ap- 
pearance presented could have occurred in any other way than as he had 
supposed. — Proceedings of the Philadelphia Academy of Science.” 
The History of the Fresh-water Algm of North America . — “ Silliman’s 
Journal ” contains a short notice of Dr. Wood’s recent work on this 
subject, which, as it is of interest, we give in full. It is now fully twenty 
years since the Smithsonian Institution performed an appropriate and most 
acceptable service by publishing the Nereis Boreali-Americana of the 
lamented Professor Harvey, thus enabling our students to study the marine 
Algce of our coasts. It proved to be one of the most popular of the Smith- 
sonian Contributions to Knowledge. The institution has now enabled our 
students, and all who are curious in microscopic life, to enter upon the more 
difficult but not less interesting investigation of the fresh-water Algce, by 
bringing out Professor Wood’s important contribution. The systematic part 
of this goodly volume consists of 239 pages, of imperial quarto size, in 
which all the United States species known to the author (exclusive of 
Hiatomacece) are arranged and described ; they are illustrated by twenty-one 
coloured lithographic plates, which appear to be excellent. A supplement 
contains six species, which are described in Professor Harvey’s ‘^Nereis,” which 
Professor Wood did not consult in season to include in their proper places; 
and in the preface a flne list of fresh-water species collected by Mr. Olney 
in Rhode Island and named a long time ago by Professor Harvey, is re- 
printed from Mr. Olney’s Algae Phodiacae.” Any student of these in- 
teresting forms may thus infer how much remains to be known of them, and 
all should unite in thanking Professor Wood in thus opening the way to 
their investigation ; also for the elaborate bibliography appended to the 
