1909] CURRENT LITERATURE 79 
phosphate, Fe;(PO,)., instead of the traces of iron which are usually added to the 
Sachs solution as Fe,Cle6. It differs from PreFFER’s and MAYEr’s essentially 
in the use of tricalcium phosphate, Ca;(PO,)., instead of potassium phosphate, 
thus avoiding the acidity of these solutions. BENECKE has tested VON DER 
Crone’s claims, some of which he finds justified, others not. The details are not 
of general interest —C. R. B 
Prochromogens.—In further development of our knowledge of plant chro- 
mogens, PALLADIN?? has found that these substances are not present in any con- 
siderable amounts at any time, but that they are formed gradually, from what he 
proposes to call prochromogens, which there is some ground for thinking are 
glucosides. These are split up by enzymes and the chromogens are produced in 
small amounts, except in the spring, when larger amounts may be observed. In 
dead plants the enzymes give rise to large amounts of the chromogens, because 
the splitting is then uncoordinated, and the oxidation of these leads to the observed 
blackening of the tissues.—C. R. B 
Light perception.—Besides the ocelli (in the sense of HABERLANDT), SCHUR- 
HOFF describes33 apparatus in six species of Peperomia which may function in the 
perception of light, namely: the funnelform palisade cells, by reflecting the light 
to the chloroplasts at their base; the upper convex wall of the palisades, by acting 
as a lens; and the cluster crystals, that disperse to all the chloroplasts the light 
focused by the lenticular upper portion of the cell. These ideas seem even more 
strained than the theory they are adduced to support.—C. R. B. 
etting of leaves.—Awano+4 furnishes the ecologists a considerable body of 
statistics regarding the wetability (there ought to be such a word, if there is not) 
of leaves. Out of 264 plants examined as to this point, he finds 164, about 4, wet- 
able with difficulty or not at all, while the rest are easily wetable. Leaves of most 
strand and sand plants are hardly wetable, while those of shade plants and ferns 
are easily wetable. The details, presented in extensive tables, are combined with 
observations on the number and distribution of stomata.—C. R. B 
Extrafloral nectaries.SALISBURY has described35 the extrafloral nectaries of 
eight species of the genus Polygonum. He ascribes the secretory action to osmotic 
pressure of the gland cells, independent of root pressure, and thinks that the nectar 
glands, which are especially striking in tropical plants, represent originally 
hydatodes, which have in some cases later acquired a biological significance. He 
3? PALLADIN, W., Ueber danice cated der pflanzlichen Atmungschromogene. 
Ber. Bowel Bot. Gesells. 2'7: 101-106. 190 
33 Scutruorr, P., Ozellen und ree > bei einigen Peperomien. 
Beih. Bot. ai 23:14-26. pls. 3 908. 
34 AWANO, S., Ueber die ues der Blatter. Jour. Coll. Sci. Imp. Univ. 
Tokyo Py bes I-49. 1909 
35 SALISBURY, E. + he extrafloral nectaries of the genus Polygonum. Annals 
of Botany 23: oncaas: fe 16. figs. 6. 1909. 
