2i8 SCIENCE PROGRESS 



germinate and the tube to grow through the tissues of the 

 style to the ovule varying from 4 to 12 days according to 

 the temperature, while if the temperature should fall below 

 zero, growth would no doubt be inhibited altogether. It is 

 thus possible during a period of cool weather for development 

 of the pollen tube to take so long that fertilisation cannot be 

 effected, as the style decays and falls off in 8 to 12 days after 

 flowering. Temperature may also have an indirect effect in 

 limiting the movements of the poHination agencies, as bees, 

 for example, do not generally leave the hive until the tempera- 

 ture reaches about iS°C., and are stated not to fly at a 

 temperature below about 5°C. 



Rain acts on the production of fruit by closing the anthers 

 or preventing them from opening, so that dissemination of 

 pollen is prevented. If pollination is once effected rain has 

 little power to wash the pollen from the stigma, and even if 

 it should be so washed away, the stigmas will secrete their 

 viscous fluid a second time. 



Too low rainfall or other climatic influences tending towards 

 a condition of drought may also influence unfavourably the 

 production of fruit. Thus high temperature with consequent 

 high rate of transpiration, low atmospheric humidity and low 

 rainfall with consequent low water content of the soil, and 

 high winds also tending to a high rate of transpiration, are all 

 factors which may so disturb the water relations of the plant 

 that an abscission layer forms in the flower stalk so that the 

 flower or fruit is cut off and shed immaturely. (Cf. H. Molisch, 

 " Pflanzenphysiologie als Theorie der Gartnerei," Dritte 

 Auflage, 1920.) That this is the probable cause of premature 

 shedding of fruit in the Washington navel orange has been 

 shown to be the case by J. E. Coit and R. W. Hodgson {Cali- 

 fornia Agric. Exper. Sta. Bull., 290, 191 8), and in cotton by 

 F. E. Lloyd, " The Abscission of Flower Buds and Fruits in 

 Gossypium, and its Relation to Environmental Changes " 

 {Trans. Roy. Soc. Canada, Ser. 3, 10, 55-61, 19 16). 



Very interesting observations on the influence of illumina- 

 tion on flowering and fruiting have been made by W. W. Garner 

 and H. A. Allard (" Effect of Relative Length of Day and 

 Night on Growth and Reproduction of Plants," Journ. Agric. 

 Res., 18, 553-605, 1920 ; " Flowering and Fruiting of Plants 

 as Controlled by the Length of Day," Yearbook U.S. Dept. 

 Agric, 377-400, 1920) by placing potted plants in dark 

 chambers during some of the hours of dayhght and so shortening 

 the period of illumination, and by lengthening the daily period 

 of illumination by the use of artificial light at night. These 

 workers found that the flowering and fruiting stages in a 

 number of species are only reached if the length of the period 



