SCIENTIFIC SUMMARY. 
207 
the years 1853 and 1858, and to have been in some way received from the 
United States, but the manner of its coming eludes enquiry. 
The Fruiting of an Alga , Mastigonema. — In u Grevillea ” for February 
Mr. Cook, the editor, says that Dr. Wood has described, in his new and 
interesting work on the “Fresh Water Algse of the United States,” a new 
species of Mastigonema , which he calls M. fertile. His remarks upon this 
species are of interest to Algologists. He says — u I found this plant in a 
stagnant pool in ‘ Bear Meadows/ forming a filamentous, felty mass, with 
CEdogonium echihatum and other algse. The variously curved and inter- 
laced flexible filaments are always simple, and of uniform, or nearly uniform, 
diameter through their whole length ; excepting that, in some instances, 
there are small, local, bulbous enlargements of the sheath. Though the 
ends of the filaments, in all the specimens I have seen, are abruptly trun- 
cate, it is very possible that in the young trichoma the apex is prolonged 
into a long hair, as in most of the Mastigonema. The inner filament is 
sometimes very distinctly articulated ; often, however, it is not at all so. 
The sheaths are firm, not at all lamellated, and generally project beyond 
the inner trichoma. The spores are cylindrical, yellowish, with a pretty 
distinct, although very close coat. They are always enclosed in distinct 
cells, and are mostly several in a filament, placed at intervals in its length. 
u This is the first instance, at least,” says Mr. Cooke, u that I know of, 
in which a species of this genus has been found in fruit, and it is interesting 
to note the resemblance of the spores to those of the more commonly 
fruiting Rivularias.” 
The Source of Nitrogen in the Food of Plants. — A somewhat strange series 
of opinions are those that have been started by M. Deherain in his recent paper 
in the u Annales des Sciences Naturelles.” While adopting the conclusions of 
Lawes and Gilbert, Ville and Boussingault, that plants have no power of 
absorbing nitrogen directly from the air, he still holds that the atmospheric 
nitrogen is the source of that which enters into the composition of the 
tissues of the plant. The results of a series of investigations which M. 
Deherain has carried out tend to show that atmospheric nitrogen is fixed 
and retained in the soil through the medium of the hydrocarbons, such as 
humus, in conjunction with alkalies, and that this fixation is favoured by 
the absence of oxygen. In other words, the fixation of atmospheric nitrogen 
occurs when organic materials are in process of decomposition in an 
atmosphere either deprived of oxygen or in which that element is deficient. 
Under these circumstances carbonic acid and hydrogen are both given oft*, 
the latter uniting with nitrogen to form ammonia. According to the 
earlier researches of Thenard there are in soil two strata exposed to the action 
of the atmosphere — an upper oxidising and a lower deoxidising stratum. 
In the first stratum the nitrogen is obtained from the atmosphere, 
and impregnates the subjacent soil around the roots ; in the second the 
nitrogenous compounds are converted into insoluble humates. The air of 
the soil is therefore at a certain depth deprived of oxygen ; hydrogen is 
produced as the result of the decomposition of organic substances; and this 
hydrogen unites with the nitrogen to form ammonia. If these views are 
correct, they will have a considerable practical importance in agriculture, 
the value of a manure depending not so much on the actual amount of 
