1920] AGRICULTURAL. BOTANY. 821 



nishiiif,' data for more specialized studies to follow refrardlnp: the content of 

 numerous plants named in cyanoglucoslds, saponins, alkaloids, oxidases, per- 

 oxidases, and otlier principles. 



Review of the genus Arceuthobium (Razoumofskya) with particular 

 reference to its biology and practical significance, C. von Tubeuf (Naturw. 

 Ztschr. Forst u. Laiuiw., 11 (IDID), A'o. 6-9, pp. 161-278, figs. 50).— This contri- 

 bution, which treats systematically, geographically, and practically of Arceutho- 

 bium (Razoui)iofski/(i) spp. and their hosts, is in four main sections dealing 

 respectively with mistletoes and witches' brooms, mistletoes and their hosts, 

 the biology and pathology of mistletoes, and the abundant literature of the 

 subject. 



Permeability in plant cells, F. Wkkj^j (Naturw. Wchnschr., SS (1918), No. 

 7, pp. 89-95). — This is largely a synthetic and interpretative discussion of the 

 data and conclusions of others regarding osmotic relations in plant cells. 



Quantitative laws in regeneration, I, J. Loeb (Jour. Gen. Physiol., 2 (1920), 

 No. S, pp. 297-S07, figs. 4). — Regeneration, the growth of resting cells or bodies 

 following removal of parts of the body, presents problems relating to the 

 quantity of growth as measured by the mass of the regenerated parts and 

 relating also to the problem of the inhibition of such growth pending removal 

 of a portion of the body. A review is given by the author of his own studies 

 and conclusions regarding such phenomena. It is claimed that equal masses 

 of sister leaves of Bryophyllum calycinum produce equal masses of shoots and 

 roots in equal time and under like conditions. 



The mass of shoots and roots produced by different masses of sister leaves 

 in equal time and under similar conditions is approximately in direct propor- 

 tion to the masses of the leaves. 



When a piece of stem inhibits the production of shoots and roots in a leaf 

 of Bryophyllum connected with it, the stem gains in mass. This gain is equal 

 approximately to the mass of shoots and roots the leaf would have produced 

 if it had been detached from the stem. This suggests that the inhibitory 

 Influence of the stem upon formation of shoots and roots of the leaf Is due to 

 the fact tJiat the material available for this process naturally flows into the 

 stem. 



The nature of the directive influence of gravity on the arrangement of 

 organs in regeneration, J. Loehj (Jour. Gen. Physiol., 2 (1920), No. 4, pp. 373- 

 S86, figs. 9). — It has been shown in previous papers (E. S. R., 42, p. 26) that 

 the leaves of Bryophyllum calycinum suspended in moist air sidewlse. in a 

 vertical plane, form roots and shoots in the notches predominately or ex- 

 clusively on the lower side of the leaves. Stem sections develop roots generally 

 on the lower side but on both sides at the basal end. It has been suggested that 

 this directive force of gravity may be due to a combination of two factors, 

 namely, gravity (collecting more sap on the lower side), and an inhibitory 

 factor (organs growing at first or growing quickly, generally retarding or 

 Inhibiting the growth of similar organs elsewhere). 



The present paper shows that in leaves suspended in moist air a red pigment 

 is formed which tends to collect gradually in the lower parts of a vertically 

 suspended leaf, thus serving as an indicator for the distribution of the sap 

 and proving its tendency to collect in greater abundance at the lower end of a 

 leaf so suspended. It is also stated that leaves or stems of Bryophyllum sus- 

 pended as described under water develop roots on both upper and lower sides, 

 the directive force of gravity upon the organs being absent in this case, since 

 the abundance of outside water reduces the effect of a slight difference in the 

 sap distributed (as between the upper and lower side) to a negligible factor. 



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