ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 591 



General. 



Incomplete Dichogamy in Zea Mays.* — J. Burtt-Davy contributes 

 a short note upon the pollination of the Maize. The writer made 

 observations upon plants of indentata x indurata and found that 

 75 '75 p.c. of the plants were protandrous, while only 24 '24 p.c. 

 were protogynous. The numbers appear to be in Mendelian proportions, 

 and it is possible that protandry is dominant in one parent and 

 protogyny in the other. This result is contrary to that usually obtained, 

 and it is also to be noted that where dichogamy occurs in Maize, it is a 

 distinct aid in preventing self-pollination. The author believes it 

 possible that our present types of Maize are really the product of 

 hybridisation. 



Insects and the Asclepiadaceae.t — J. K. d'Herculais contributes a 

 note upon the connection between Araujia and other Asclepiads with 

 such insects as the Hymenoptera, Lepidoptera, and Diptera. The 

 writer has had many opportunities of observing the visits of insects to 

 these flowers, and does not agree with the usual opinion as to the use of 

 insects in bringing about pollination. Between each pair of stamens is a 

 well-formed groove, expanded at the base but narrowing towards the 

 upper end, and connected with this groove is a spout-like, elastic retina- 

 culum. When an insect inserts its proboscis into the nectary, it is thus 

 unable to withdraw it, but hangs helplessly until it dies of exhaustion. 

 When the flower is mature the insect can visit it with impunity and 

 remove the pollinia, but it is remarkable that the visits are then less 

 frequent. The role of insects in effecting pollination is probably much 

 less important than is usually supposed. 



CRYPTOGAMS. 



Pteridophyta. 

 (By A. Gepp, M.A., F.L.S.) 



Alternation of Generations.^ — V. H. Blackman publishes a 

 criticism of W. H. Lang's recently promulgated theory as to alternation 

 of generations and ontogeny, and discusses particularly the question of 

 the physiological reason for the difference of gametophyte and 

 sporophyte. He does not accept Lang's view that the egg and the 

 spore develop so differently as a result of external conditions ; that the 

 egg, being protected and nourished in the archegonium, becomes the 

 large differentiated sporophyte, while the spore, cast loose on damp 

 earth, produces the small prothallus. He believes rather that the 

 various stages are united together by a cyclical correlation, one stage 

 influencing the development of the other (but he does not attempt to 

 explain the mode of origin of the two generations). He cites in 

 illustration the life-cycle of Pucctnia graminis, the metamorphosis 



* Journ. of Bot., xlvii. (1909) pp. 180-2. 



t Comptes Bendus, cxlviii. (1909) pp. 1208-10. 



t New Phytologist, viii. (1909) pp. 207-18. 



