ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 561 



Respiration in Leaves attacked by Peronospora.* — L. Pavarino 

 finds that normal respiration is accelerated by the presence of Peronospora 

 in the tissues ; the absorption of oxygen is increased. Intra-molecular 

 respiration is more active in diseased leaves, but it becomes exhausted, 

 while it continues in healthy leaves. He finds also an increased quantity 

 of oxydase not only in leaves invaded by a parasite but also in wounded 

 leaves. This is due, he considers, to the reaction of the protoplasm 

 against the parasite or the poisonous substances excreted by it. The 

 experiments were made on vine-leaves. 



Terry, O. P. — Galvanotropism of Volvox. 



Amer. Joum. of Physiology, xv. (1906) pp. 235-44. 



General. 



Graft Hybrids.! — Noll, having examined the graft-hybrids resulting 

 from grafting Mespttus germanica upon Crataegus monogyna, is of the 

 opinion that they originate through nuclear fusion in the callus. The 

 cells of the hybrid branches have not double the sporophyte number of 

 chromosomes, so that if these branches arose from fusion of two vegeta- 

 tive cells, there must have been some method of reduction. The greater 

 resemblance of the hybrid to the stock or scion is explained by the 

 assumption that in each fusion the nucleus which moved into new 

 cytoplasmic surroundings was so weakened that in the reduction process 

 it contributed fewer determinants than did the stationary nucleus to the 

 hybrid nucleus. The author hopes to succeed in recreating the hybrid 

 Laburnum Adami, which is said to give similar results. 



Nectaries of CruciferaB.ij: — Armando Villani finds that the nectaries 

 of Cruciferge are referable to one primitive type, viz., two at the base, 

 external to each stamen, constituting a dimerous, external whorl, and 

 two at the base, and between each member of each pair of long stamens, 

 constituting an internal dimerous cycle. The author thinks that the 

 Cruciferas may be divided into types and generic groups according to 

 the number and position of their nectaries. He regards the whole flower 

 as dimerous, the tetramery of the corolla being only apparent. 



Variation of Flowers.§ — Gr. Klebs, as a result of experimental work 

 on the variations of flowers, offers a substitute for De Vries's intracellular 

 pangenesis. He is convinced that all variations are due to the influence 

 of external factors upon the inherent potentialities of the organism, and 

 has made use of various conditions of temperature, darkness, wounding, 

 and artificial food, using Campanula Trachelium and Semper vivum Funkii 

 for his experiments. He shows that the taxonomic limits of a given 

 species are easily passed if external conditions favour the expression of 

 potentialities inherent in the organism. The influence of external con- 

 ditions is much greater before inception of the organs than after. He 



* Atti 1st. Bot. Pavia, xi. (1906) p. 16. See also Bot. Centralbl., cii. (1906) 

 pp. 38-9. 



t SB. Niederrhein Ges. Nat. u. Heilkunde, Bonn (1905). See also Bot. Gaz., 

 xli. (1906) pp. 358-9. J Malpighia, xix. (1906) pp. 399-439. 



§ Jahrb. wiss. Bot. xlii. (1906) pp. 155-320 (1 pi.). 



