THE MICROBIOLOGY OF THE ATMOSPHERE 



may delay both extrusion of the stamens and splitting of the anthers. 

 Except for rye and maize, most cultivated cereals are self-fertilized and 

 shed little pollen, but pasture grasses are free shedders. 



In central Europe, Marilaun (1895) found that different grasses 

 flowered for brief periods of only 1 5 to 20 minutes daily, and at charac- 

 teristic times of the day : 



hours 



04-05 Poa, Koeleria, Avena elatior. 



05-06 Briza, Deschainpsia caespitosa, Triticiim, Honleum. 



06-07 Secale, Dactylis, Andropogon^ Brachypodiian, {Bromiis?), Festtica spp., 



Hole us (ist anthesis). 



07-08 Trisetiiin, Alopecurus, Phkiini, Anthoxanthum. 



08-09 Exotic types in Europe: Paniciiiii, Sorghum. 



09-10 Set aria italica, Gynerium (Cortaderia) argenteum. 



11-12 Agrostis spp. 



12-13 Melica, Molinia, Nardiis, Elymus, Sclerochloa, some Calamagrostis spp. 



14 A few B ramus spp. 



15 A few Arena spp. 



16 Agropyrum. 



17-18 Deschampsia flexuosa . 



19 Hokus (2nd anthesis). 



This timetable does not necessarily apply elsewhere, and, in Nebraska, 

 Jones & Newell (1946) found a less precise timing and showed that 

 anthesis is determined by temperature. They distinguish cool-season 

 from warm-season grasses. Cool-season grasses include: Fcstuca elatior 

 (anthesis at 13.30-15.00 hours); Agropyrum spp. (14.00-18.30 hours); 

 Bromus inermis (14.30-19.00 hours); Poa pratensis (during the night); 

 Secale cereale (02.30-11.30 hours, maximum 06.00-08.30 hours). The 

 warm-season group includes: Boiitcloua gracilis (03.00-09.00 hours, maxi- 

 mum 04.30-05.30 hours during darkness) ; ^m^A/oV dactyloides (06.30-13.00 

 hours, maximum 07.00-08.30 hours); Paniciini virgatum (10.00-12.00 

 hours, delayed in cool season); Zea mays (07.30-16.00 hours, maximum 

 08.30-11.00 hours). 



Hyde & Williams (1945, p. 89), from the cooler climate of Wales, 

 report both discrepancies and agreements with Marilaun's timetable: 

 Holcus lanatus (04.00-06.00 hours, but mainly at 14.00-19.00 hours); 

 Cynosurus cristatus (05.00-06.00 hours); Arrhenatheriim (07.00-08.00 

 hours); Trisetum flavescens (before 08.00 hours); Festuca pratensis (08.00- 

 14.00 hours). 



(ii) Aquatic monocotykdonous herbs include a few other wind-pollinated 

 plants, for example Triglochin and Sparganimn, while in the genus 

 Potamogeton some species are pollinated by wind and others by water. 



(iii) Entomophilous herbs and low shrubs include some species in which 

 the phase of insect visitation is followed by an opportunity for wind- 

 pollination, the anthers first shedding pollen within the corolla; but as the 

 flower matures, the elongating filaments protrude and scatter pollen in the 

 wind. These types include the semi-parasites Bartsia and Lathraea 



42 



