SCIENTIFIC SEMMAKY. 
205 
A Monograph on the Genus Fyrus . — M. Decaisne has recently published a 
valuable monograph on the genus Pyius, with a full generic character, and 
descriptions and figures of the races, as he would term them, considering as 
he does all known forms of the restricted genus as a single and very poly- 
morphous species. The six races are : 1. The Celtic, Proles Armoricana, 
of three quasi-species, P. cordata, Poissieriana, and longipes. 2. The Ger- 
manic, Proles Germanica, or Pyrus communis, including our common pears, 
both pear-shaped and apple-shaped, “ both forms being often met with upon 
the same tree.” Under this head (says a reviewer in Silliman’s 
Journal ”) Professor Decaisne gives some interesting pages upon the history 
of the cultivation of pears in France, which cannot be ancient, and of cider 
(perry) as a drink. It appears that it took the place of beer in the north 
of France in the fifteenth century or later, and is now giving way to wine 
and perhaps beer again ', and that pears would have disappeared before this 
from a part of Normandy, were it not that they are carried in immense 
quantities to Epernay, where they are used in the manufacture of champagne. 
3. The Hellenic race, which comprises P. parviflora and three other sub- 
species. 4. The Pontic race, P. salicifolia and its allies. 5. The Indian 
race, P. Pashia and its relatives. 6. The Mongolian race, P. Sinensis and 
its varieties. As one turns over the excellent plates one can hardly be 
persuaded that such extremely diverse forms can practically be regarded as 
of one species. A list of the species remanded from Pyrus to other genera 
shows that the result of our author’s prolonged and sagacious study is to 
I increase the genera about as much as he diminishes the species of the 
Linnaean Pyrus. 
What Parts of Chlorophyll-bearing Plants exhale Oxygen. — Professor 
' Draper, of New York, in a recent paper on “ Evolution in Seedlings,” says 
that of the chlcrophyll-bearing plants it is found that in the Phanerogamia 
! it is only the gi'een parts that at any time exhale oxygen, and then only 
* under the influence of sunshine. The other parts of the plant above the 
ground, that are not green, viz., the stem, twigs, flowers, &c., are at all 
times, day and night, exhaling carbonic acid. The whole history of the 
plant, from the time the seed is planted to its death, is a continuous story 
of oxidation, except when sunlight is falling on the leaves. The seed is put 
into the ground, and during germination oxygen is absorbed and carbonic 
i acid exhaled. If the seedling is kept in the dark, oxygen is never exhaled, 
only carbonic acid, and the plant not only grows, but all visible structures 
i except flowers are formed in a rudimentary condition. In the light the 
! growth during the night time is attended by the evolution of carbonic acid, 
' while during the day time the bark of the stem and branches is throwing 
I off carbonic acid. When flowers and seeds form, the evolution of carbonic 
acid attending this highest act of which the plant is capable is often greater 
! than that produced at any time in many animals. Hence the author con- 
; eludes by saying that “ Everything in the history of plants, therefore, tends 
to show that the evolution of their structures' is inseparably attended by 
! the formation of carbonic acid, and it seems impossible, when we consider 
\ the evolution alone, to arrive at any other opinion than that already 
expressed — that, all living things, whether plant or animal, absorb oxygen and 
