ABSORPTION OF MATERIALS IN GENERAL I17 



membrane into the solution below, where it can be identified with suitable 

 chemical reagents. 



Czapek^ studied the nature of root excretions. He employed plates made 

 of a mixture of aluminium phosphate and plaster of Paris. These are soluble 

 in many acids (hydrochloric, nitric, sulphuric, phosphoric, formic, oxalic, suc- 

 cinic, lactic, malic, citric, and tartaric) but they are insoluble in carbonic, 

 acetic, propionic and butyric acids. Various kinds of roots produced no effect 

 upon these plates, when they were exposed to the roots as was the marble men- 

 tioned above, and it therefore follows that acids belonging to the first list just 

 given are not noticeably present in root excretions. In other experiments by 

 the same writer Congo red was employed, which becomes brownish-red through 

 the action of carbonic acid and bright blue through the action of acetic, pro- 

 pionic and butyric acid. The roots turned the Congo red only brownish-red, 

 without any tendency toward blue, from which it appears that the corrosion 

 of the marble (in the experiment described above), and of soil particles, 

 is to be attributed to the action of carbonic acid excreted by the roots. 

 According to Stoklasa and Ernest^ roots excrete organic acids only when 

 inadequately supplied with oxygen. 



The following examples indicate how much may be accomplished by plants 

 in dissolving soil particles. Lind' showed that the hyphae of certain fungi in 

 pure cxilture were able to penetrate through marble plates and bones. Nadson* 

 described a considerable number of algae that penetrate somewhat deeply into 

 limestone and shells, dissolving the material. These forms experience severe 

 competition with many other algae on the surface of the substratiim, but their 

 ability to grow in solid limestone, which is impenetrable to their competitprs, 

 gives them a definite advantage in the struggle for existence. Nadson found 

 that these algae excrete oxalic acid.^ 



It is also well known that parasitic fungi penetrate the cell walls of their 

 host plants. Miyoshi* found that fungus hyphae can pierce membranes of very 

 different kinds. The membranes to be studied were placed over nutrient gela- 

 tine and inoculated with spores. As germination took place the hyphae bored 

 through the membranes and reached, the nutrient media below. 



1 Czapek, Friedrich, Zur Lehre von den Wurzelausscheidungen. Jahrb. wiss. Bot. 29 : 321-390. 1896. 



' Stoklasa, Julius, and Ernest, Adolf, Beitrage zur Losung der Frage der chemischen Natur des Wur- 

 zelsekretes, ■ Jahrb. wiss. Bot. 46: SS— 102. 1909. 



*Lind, K., Ueber das Eindringen von Pilzen in Kalkgesteine und Knochen. Jahrb. wiss. Bot. 32: 

 603-634. 1898. 



' Nadson, G., Die perforierenden (kalkbohrenden) Algen und ihre Bedeutung in der Natur. [Abstract 

 in German, pp. 3S-40. Text in Russian.] Scripta Botanica Hort. Univ. Imp. St. Petersburg 18: i -40. 

 1900-1902. 



'Miyoshi, Manabu, Die Durchbohrung von Membranen durch Pilzfaden. Jahrb. wiss, Bot. 28: 

 269-289. 1895. 



" Also see: Diels, L., Die Algen- Vegetation der Siidtyroler Dolomitenriffe. Ber. Deutsch. 

 Bot. Ges. 32 : 502-526. 1914. — Ed. 



