ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 451 



cylinder in the radicle mark the limit of suspensor and embryo, the 

 lower cortex and root-cap are derived from the suspensor. In the Ivy 

 secretory canals are found in the pericycle, appearing first in tlio hypo- 

 cotyl, while tracheids arise only in the cotyledons. The embryos of 

 other members of this order show neither canals nor tracheids. 



Parthenogenesis in Thalictrum purpurascens.* — J. B. Overton 

 describes this phenomenon and discusses parthenogenesis in seed-plants 

 generally. 



He finds the development and germination of the megaspore in 

 Thalictrum to be that usual among angiosperms. The antipodal cells 

 are remarkably large, and their nuclei multiply by fragmentation. 

 Fusion of the polar nuclei occurs before fertilisation in normal material, 

 and before the division of the egg in parthenogenetic material ; the 

 definitive nucleus is remarkably large. Fertilisation is not necessary 

 either for embryo or endosperm development. Embryos were produced 

 parthenogenetically under all conditions. Parthenogenesis is very 

 general ; the development of the embryo is the same as in the case of 

 embryos formed from a fertilised egg. Loeb's work on eggs of echino- 

 derms showing that unfertilised eggs may be made to develop into 

 normal embryonic forms through increase in osmotic pressure, suggested 

 an explanation of the present case. The egg is invested in early stages 

 by a dense sheath of cytoplasm, and later becomes surrounded by an 

 area much resembling a vacuole, which may affect the osmotic pressure 

 and indicate a withdrawal of water causing the oosphere to divide. The 

 author discusses previously described cases of parthenogenesis in angio- 

 sperms and suggests that it is of more common occurrence than at 

 present supposed. 



Physiology. 

 Nutrition and Growth. 



Green Hemiparasites.| — E. Heinricher supplements his previous 

 observations on Euphrasia, Odontites, and Alectorolophus. He describes 

 culture experiments made with Euphrasia with a view of ascertaining 

 whether the chemical properties of the cell-sap were prejudicial to a 

 plant serving as a host. He finds that species of Euphorbia and Oxalis 

 served admirably as host plants in spite of the peculiar chemical 

 qualities of their cell-sap. The culture of Euphrasia minima confirmed 

 the previous suggestion that this plant was relatively independent — 

 many of the specimens reached the flowering stage without becoming 

 parasitic. 



With regard to Alectorolophus, he shows that Koch's statement, that 

 monocotyledons exclusively could serve as host plants, is wrong since, as 

 in Euphrasia, dicotyledons also will serve. He cultivated three species 

 of the parasite on widely different hosts, such as Origanum vulgare, Poly- 

 gonum aviculare, Veronica, Lotus, Stellaria media, &c, obtaining perfect 

 development in each case. He also shows that with Alectorolophus, as in 

 the case of Euphrasia, the same individual may attach itself at the same 

 time to the roots of very different hosts. A series of cultures was also 



* Bot. Gaz., xxxiii. (1902) pp. 363-75 (2 pis.). 



t Pringsh. Jalirb. Bot., xxxvii. (1902) pp. 2G4-337 (2 pis.). 



