POLLARDING 



623O 



POLLINATION 



Protector Somerset, 1900; Henry 

 VTII. 1902 and 1913 ; Vol. VI of 

 The Political History of England, 

 1910; The Reign of Henry VII, 

 1913-14 ; A Short History of the 

 Great War, 1920. He contributes 

 Parliament and several other arti- 

 cles to this encyclopedia. See 

 portrait gallery of contributors. 



Pollarding. Removal of all 

 the branches at the head or poll 

 of a tree, in order to induce the 

 stem to throw out fresh branches. 

 The custom is usually resorted to 

 in districts where fuel is scarce. 

 See Forestry. 



Pollen (Lai., fine flour, mill- 

 dust). Mealy substance, mostly 

 yellow, which fills the anthers of 

 flowering plants and grasses. The 

 grains of which it is composed con- 

 tain the male elements or nuclei, 

 which fuse with the female ele- 

 ment in the ovules enclosed in the 

 carpels or ovary. This fusion 

 brings about the formation of an 

 embryo which, with its wrappings, 

 constitutes the seed. 



In plants that are pollinated by 

 the wind the pollen grains are dry 

 and light. Most forest trees are 

 so pollinated, and the pollen may 

 have to be carried a long distance 

 by the wind. In other cases the 

 pollen-grain is variously roughened 

 that it may the more easily catch 

 upon the hairy bodies of the in- 



sects that act as pollen-carriers. 

 In the orchids the pollen-grains 

 have long threads which are united 

 to form a stalk to the pollen-mass 

 (poll iniu in ). 

 which may be 

 carried away 

 bodily by at- 

 tachment to 

 the head of a 

 visiting insect, 

 so that it is 

 placed on the 

 stigma of the 

 next orchid 

 visited. See 

 Bee ; Flower. 

 Pollen, ARTHUR JOSEPH HUNGER- 

 FORD (b. 1866). British author. A 

 son of John Hungerford Pollen, he 

 was educated at the Oratory 



A. J. H. Pollen, 

 British author 



/!u 'ih Cecil 



School, Birmingham, and at Trin- 

 ity College, Oxford. He became a 

 barrister, but, devoting himself 

 largely to naval matters, was the 

 pioneer of a system of fire control. 

 He wrote extensively on the navy, 

 and among his books are The Navy 

 in Battle, 1918. r 



Pollenzo. Town ot Italy, the 

 ancient Pollentia. It stands on the 

 Tanaro, 30 m. from Turin, and has 

 remains of an aqueduct, amphi- 

 theatre, temples, etc. Here, in 

 403, Stilicho defeated Alaric and 

 the Goths. 



Pollination. Process antece- 

 dent to the fertilisation of the 

 ovules of a flower, by which the 

 pollen-grains produced in the 

 anthers are brought to the stigma, 

 where they are stimulated into 

 activity and emit a long shoot 

 which penetrates into the ovary 

 and enters the ovules, thus effect- 

 ing fertilisation. 



In the simplest form of pollina- 

 tion, known as autogamy, or self- 

 pollination, and found in many of 

 the commonest weeds, the anthers 

 are so situated in relation to the 

 stigma that the pollen fertilises the 

 ovules of the same flower. In the 

 majority of plants, however, means, 

 often elaborate, are taken to pre- 

 vent self-pollination, and to obtain 

 the aid of external agents in effect- 

 ing cross-pollination To this end 



Pollen. Highly magnified specimens bom British trees and plants. 1. Cedar of Lebanon. Cedrus libani, showing air-sacs. 

 Z. Willow Herb, Epilobinm angustifolium. 3. Lupin, Lupinus. 4. Thistle species. 5. Sage, Salvia officinalis. 6. Evening 

 Primrose, Oenothera biennis. 7. Sweet Pea, Lathyrus odoratus. All are magnified 66 times except 3 and 5, whicb 



are magnified 100 times 



