DIV. n SPERMATOPHYTA 553 



anthers of Gramineae on long slender filaments has the same significance. 

 The pollen grains of anemophilous flowers also have characteristic 

 features. They are light and smooth, and in some Conifers are even 

 provided with two wing-like sacs (Fig. 510 D), which enable them 

 to remain suspended longer in the air. Some Urticaceae (Pilea, 

 Urtica) scatter the pollen on the opening of the elastically-stretched 

 wall of the pollen sac as a light cloud of dust. 



The female flowers are usually not brightly coloured and do not 

 develop nectaries. The stigmas, which catch the pollen, are strongly 

 developed and provided with long feathery hairs (Fig. 527), or their 

 form is brush-like, pinnate or elongated, and filamentous. In many 

 Gymnosperms (e.g. Taxus) the macrosporangium excretes a drop of 

 fluid in which the pollen grains are caught ; on drying up of the drop 

 the pollen is drawn down on to the tip of the 

 nucellus. In other cases the pollen grains glide 

 down between the carpellary scales of the cones 

 till they reach the moist micropyles of the 

 ovules and adhere to them. 



Lastly, the time of flowering is not without 

 importance. The Elm flowers in February and 

 [March long before its leaves develop, and the 

 same holds for the Hazel, Poplar, and Alder. 

 In the Walnut, Oak, Beech, and Birch the 

 flowers open when the first leaves are unfolding, 

 and flowering is over before the foliage is fully 

 expanded. Were this not so, much of the 

 pollen would be intercepted by the foliage leaves, 

 and even more pollen would need to be produced 

 than has to be done to ensure fertilisation. In ^ 526 _ Catkin of Corylus 



the Conifers the foliage presents less difficulty, americana. (After DUCHARTRK.) 



but here the female cones are borne at the 



summit of the tree (Abies) or high up (Picea), while the male flowers are 

 developed on lower branches. The pollen grains are shed in warm 

 dry weather, and carried up in the sunshine by ascending currents 

 of air till they reach their destination on the female cones situated high 

 above the male flowers. 



Only a small number of Phanerogams make use of the agency of 

 water for effecting their pollination, and are, on that account, termed 

 HYDROPHILOUS PLANTS. This applies only to submerged water plants 

 which do not emerge from the medium, e.g. Zostera, Seawrack. 



The great majority of Phanerogams are dependent upon animals, 

 especially on insects, for the transference of their pollen. Plants 

 pollinated by the aid of insects are termed ENTOMOPHILOUS. 



Since KONRAD SPRENGEL in his famous work, Das entdeckte 

 Geheimnis der Xafnr im Ban und in der Befruchtung der Blumen, 1793, 

 revealed the mutual relations between the forms and colours of flowers 



