432 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Acid Excretion of Roots.* * * § — Herr F. Czapek has investigated the 
nature of the acid substances contained in the fluid excreted from the 
roots of a variety of plants. Of inorganic bases, potassium was found to 
be invariably present, magnesium very often, calcium only rarely. Small 
quantities of chlorides were often found, phosphates invariably, and the 
acid reaction was due to the presence of potassium orthophosphate. 
Of organic acids, formic was often found in the form of potassium 
formate, oxalic acid only in the hyacinth, and then only in the form of 
potassium orthoxalate. The corrosive action of roots on mineral 
substances was found to be in all cases due to carbon dioxide. 
Acidity of Root-Sap.f — Mr. F. H. Perry Coste gives a summary of 
the recent method of estimating the amount of potash and phosphoric 
acid contained in soils, that is actually available as plant-food. The 
object being to decide what strength of (organic) acid solution should be 
used in the analytical process of extracting soils, so as to correspond 
with the acidity of roots, this acidity was estimated in between 50 and 
60 species of 20 natural orders — special attention being paid to Cruci- 
ferae, Leguminosae, and Gramineae. The acidity is calculated into 
(A) terms of hydrogen, (B) of citric acid. 
Percentage of Acidity in Sap 
in terras of 
Hydrogen. Citric Acid. 
Gramineae (average of 16 species) *0055 *38 
Cruciferse (average of 25 determinations in 13 species ’0085 *60 
and varieties). 
Leguminosae (average of 5 species : 9 determinations) . . * 0094 • 66 
Umbelliferse (average of 4 species) *0079 *55 
Onagracem (CEnotliera) *0220 1*54 
Kosaceae ( Geum and Strawberry : 4 determinations) .. *0348 2*43 
The last family is unique in its high acidity, and in Geum this was 
found in one case to be as high as 3 * 69, that of the strawberry reaching 
1 *5 (in terms of citric acid). The acidity in Armeria (Plumbaginacete) 
is nearly as high as that in Onagracese. 
(3) Structure of Tissues. 
Resin-Passages of Coniferse.j: — Herr S. Rywosch points out a corre- 
lation between the position of the resin-passages and the development of 
the hypoderm in the two-leaved species of Pinus. If the latter tissue 
consists of several layers, the passages are completely imbedded in the 
chlorophyll* layer ; if of only a single layer, they lie outside it. In the 
former case resin-passages occur also within the protecting sheath, and 
therefore in the central cylinder, one or two in each leaf close to the 
protoxylem ; they are much smaller than those outside the sheath. 
Anatomy of Artocarpus.§ — Herron E. Pfitzer and A. Mayer find 
several peculiarities in the anatomical structure of the inflorescence and 
fructification of Artocarjpus integrifolia. In the stalk of the ripe fructi- 
fication, the horseshoe-shaped vascular-bundle-system is broken up into 
a large number of circular fragments arranged irregularly on the trans- 
* Ber. Deutsch. Bot. Gesell., xiv. (1896) pp. 29-33. 
t Nat. Sci., 1896, pp. 312-7. 
J SB. Naturf.-Gesell. Dorpat, x. pp. 517-8. See Bot. Centralbl.. lxvi. (1896) p. 67. 
§ Ber. Deutsch. Bot. Gesell., xiv. (1896) pp. 52-3. 
