ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 335 



Chemical Changes. 



Blackening" of Green Leaves.* — L. Maquenne and Demoussy con- 

 tribute a further note upon the causes of the blackening of leaves. The 

 plants used for experiment were the fig and privet, which are very 

 sensitive to electric light, and the ivy and Aucuba, which are less so. 

 The experiments included the plunging of a portion of the leaf into 

 hot or boiling water for a short time, or treatment in an atmosphere of 

 chloroform vapour. In both these cases blackening of the portion of 

 leaf thus treated took place slowly when exposed to electric light. Al- 

 though it appears probable that the phenomenon is of diastatic origin, it 

 cannot be proved that any oxydase takes part in the reaction. If the 

 leaves are completely immersed in the hot water, so as to destroy all 

 diastases contained in the leaf, no blackening results under the influence 

 of electric light. The present experiments confirm the previous con- 

 clusions of the author, viz., that blackening of the leaf is not a specific 

 result of the ultra-violet rays but is also brought about by heat, action 

 of chloroform, and mechanical bruising, all of which kill the protoplasm, 

 and bring about a mingling of the cell-sap. The phenomenon is the 

 result of diastatic action. 



General. 



Williamsonias of Mixteca alta.f — G-. R. Wielaud has examined the 

 fossils of the Rhat-Liassic beds of the plateau and mountain region of 

 the Mixteca alta in Mexico. These beds are about 2000 feet in thickness 

 and contain abundant fossils, of which the most noteworthy are the 

 imprints and moulds of numerous fruits of Williamsonia, together with 

 fronds and seeds of Zamites, Otozamites, Podozamites, Pterozamites, 

 Ptilophyllum, and Dictyozamites. One Williamsonia strobilus with 

 ovulate fruit resembles Buckland's Podocarya. A number of buds 

 inclosed in ramentum-covered bracts have also been found. Other 

 important discoveries include small fruits on slender stems, fruits with 

 broad, thin, blade-like bracts, and a staminate disc with small niono- 

 pinnate rachises bearing two lateral rows of synangia. The author 

 believes that we are approaching the solution of the evolution of the 

 Angiosperms. " The primitive semi-Cycadean ancestor, with its crown 

 of reduced, mono-pinnate, spirally inserted microsporophylls," of Arber 

 and Parkin may be supposed to have given rise to the flowers of 

 Cycadeoidea. The present type may be one of several intermediate 

 stages culminating in the gamopetalous Angiosperms. The carpels may 

 be supposed to have evolved in a similar way. The author inclines to 

 the opinion that the petals result from more or less completely sterilised 

 sporophylls. After brief allusions to cruciferous flowers, etc., in support 

 of his theory, the author shows that the form of foliage, stem-structure, 

 etc., offer no obstacles to the connection of the modern angiospermous 

 types with primitive seed-bearing plants. The evidence appears to point 

 to a polyphyletic origin. 



Characters of Graft- hybrids. J — E. Strasburger contributes a paper 

 dealing with the question of graft-hybrids and the causes of the charac- 



* Gornptes Rendus, cxlix. (1909) pp. 957-61. 

 t Bot. Gaz., xlviii. (1909) pp. 427-41 (10 figs.). 

 X Ber. Bot. GeselL, xxvii. (1909) pp. 511-28. 



