December, 1909. J 



527 



Scientific Agriculture 



plants much in the way in which Cohu 

 has shown, calcium carbonate is depo- 

 sited in the Sprudelstein of Carlsbad.* 



Bacteria have been studied principally 

 from the standpoint of disease in man 

 and animals, but recently the attention 

 of agriculturists has been directed to 

 the nitrifying organisms. The first step 

 in fixation of atmospheric nitrogen is 

 accomplished by certain flagellate cells 

 called Nitrosomonas, belonging probably 

 to the animal kingdom ; these are suc- 

 ceeded by minute rod-like bacteria called 

 Nitrobacteria, which oxidise the product 

 of the former into nitrates. These 

 latter live principally, or perhaps more 

 properly should be described as having 

 been detected living in the root nodules 

 of clover, peas and similar leguminosae, 

 and have been called Rhizobium legumi- 

 nosum; they are occasionally found on 

 the roots of forest trees, and it is now 

 recognised that bacteria with similar 

 functions live free in the soil. Another 

 nitrifying organism is the Azotobacter 

 chroococcus, which lives on the leaves 

 or trees, and causes leaf mould to be so 

 rich in nitrogenous compounds.! Some 

 of the bacteria and some of the ferments 

 also have the power of undoing the work 

 of these nitrifying bacteria ; they deni- 

 trify and liberate nitrogen from nitrates. 

 The fact is familiar to gardeners in the 

 case of fresh stable manure, where the 

 action is brought about by denitrifying 

 bacteria, whereas from rotted manure 

 the deleterious organisms are absent. £ 



Regarding the action of the blue-green 

 algae in forming soil Fritsch has accumu- 

 lated a large amount of information. § 

 In a large tank at Nalande in Ceylon the 

 first forms to secure a foothold on the 

 bare rock were found to be red-coloured 

 gelatinous species of the genera Gloeo- 

 capsa and Aphanocapas ; then, when a 

 resting-place is secured, an adhesive 

 species, Phormidium taminosum, grows 

 upon it, covering large portions of the 

 rock surface with huge thin papery films. 

 Tangled filaments of Scytonema develop 

 out of the Phormidium, and tufts of 

 Tolypothrix succeed these. Treub, who 

 visited KraKatoa after the eruption of 



* F. Colin, Neues Jahrab. 1863, p. 580 ; see 

 also W. H. Weed. The formation of. Hot-Spring 

 Deposits, Internal. Conqr. Geol, Gompte, Rendu, 

 5th Sess. 1898, p. 360.' 



| A. D. Hall, Recent Developments in Agri- 

 cultural Science, Addresses and Papers, British 

 and South Africa Association Advancing Science. 

 Johannesburg, 1905, Vol. i. p. 103. 



X R. Burri and A. Stutzer, Centr.j. Bald. (2), 

 Vol. i. 1895, p. 442 



§ F. E. Fritsch, The R64e of the Algal Growth 

 in the Colonisation of New Ground, Geogr. 

 Journal, Vol. xxx. 1907, p. 531. 



1883, found the ground covered with a 

 thin, gelatinous, hygroscopic layer of 

 blue-green algaa of which the genera 

 Tolypothnx, Anabcena, Symploca, and 

 Lyngbya were the first to appear on the 

 bare rock. These growing on the 

 volcanic ash and pumice, of which the 

 whole island was composed, gradually 

 formed a soil on which higher plants 

 could grow.* 



Welwitsch describes a similar growth 

 of algaa on the " Black Rocks" of Pungo 

 Andongo, in Angola. These black rocks 

 owe their colour to the abundant growth 

 of a sub-aerial alea, Scytonema myochrous 

 var. chorographicum, which generates 

 and multiplies so rapidly during the 

 rainy season that the upper portions 

 of the mountains are covered with it in 

 a very short while. Soon after the hot 

 seasou has set in, at the end of May, the 

 black plantlets begin to be discoloured 

 by the intense heat. They gradually 

 become dry and brittle, until they peel 

 off entirely by-and-by, after which the 

 rocks loose their sombre aspect and 

 reappear a their natural grey-brown 

 colour. t Bohlin had described four 

 algae in the Azores living on the volcanic 

 rocks in a similar waj r 4 



The blue-green algae are, however, 

 semi-aquatic, and they can only live in 

 moist places ; when, however, they are 

 joined with a fungus symbiotically to 

 form a lichen, the weft or the mycelium 

 of the fungus protects them sufficiently 

 from desiccation, and the blue-green 

 algae are rendered practically independent 

 of moisture. Welwitsch describes how 

 in the sandy valley of Cuanza River, in 

 Angola, a Blue-green alga, Porphy- 

 rosiphon notarisii extends over wide 

 meadows. By reason of its hygroscopic 

 nature, it absorbs the atmospheric 

 moisture during the dewy nights, 

 affording by this means a refreshing 

 protection to the roots of the larger 

 plants during glowing heat of the day. 

 Boodle has described a more vigorous 



* M. Treub, Notice sur la nouvelle Flore de 

 Krakatoa, Ann, Jard. Bot. Buitenzorg, Vol. vii. 

 1888, p. 213; see also Penzig, lot ci. Vol. xviii. 

 1902, p. 92. 



f F. Welwitsch, Journ. of Travel an Nat. 

 Hist. Vol. I. i. 1868; see also Apontamentos 

 Rhyto-Geographicos solve a flora da provincia 

 de Angola, etc., Annaesdo Conselho Ultramarino, 

 Parte nao off, Ser. i. Dez 1858. p, 533 ; also E. 

 Tenzl, Bericht iiber einige der wichti Ergebnisse 

 der Bereisung der Portugiesischen Kolonie von 

 Angola in den Jahren 1850-1860 durch Dr. F. 

 Welwitsch, Vienna, 1864. 



% F. Bohlin, Etude sur la Flore algologique 

 d'eau douce des Acores, Bib. K. Svenska vet. 

 Ak. Handl. Vol. xxvii, Afd. iii. No. 1 p. 



