722 MICROSCOPIC STRUCTURE OF PHANEROGAMIC PLANTS 



upon ;i l>l;ick .surface. They are then, when properly illuminated, 

 most beautiful objects for objectives of -, 1-, H-, or 2-in. focus, 

 especially with the binocular microscope. 1 



There are, in fact, few more interesting objects for the young 

 mici'oscopist than pollen-grains, both from the ease with which they 

 can always be procured, and the almost infinite variety and beauty 

 in their forms. Some of the commonest weeds, such as the dandelion 

 and groundsel, are distinguished by the beauty of their pollen-grains. 

 The grains are sometimes nearly or quite spherical, as in the hazel, 

 birch, or poplar; or of very irregular outline, as in many grasses. 

 But the most common form is elliptical, with three or five longi- 

 tudinal furrows, as in the wallflower, hyacinth, and crocus, the 

 surface being sometimes covered with warts, as in the snowdrop. 

 In the fuchsia they are triangular. In addition to the mallow and 

 hollyhock, spiny pollen-grains occur in the groundsel, dandelion, 

 ( '//teraria, and many other plants. Sometimes the grains are united 

 together by delicate threads, as in the Rhododendron and FH<-}IX/<I ; 

 and this union is much more complete in the Orchidece and Ascle- 

 / 1 iinJ >!'-. where the whole of the pollen in each anther-lobe is glued 

 together by a viscid substance into a club-shaped y^//* nun, or pollen- 

 ma. In what are called anemophilous flowers, in which the pollen 

 is carried through the air by the agency of the wind, the grains are 

 Miiall. light, dry, and usually spherical ; while in entomophilous 

 flowers, the pollen of which is carried from flower to flower by 

 insects in search of honey, the various forms above described, and 

 many others, are adapted to cause the grains to adhere to the hairy 

 under side of the body of the insect, and thus promote their dis- 

 persion. The various species of fjpilofi/inn (willow-herb) and 

 (Enothera (evening primrose) are very favourable objects for ob- 

 -ervir.g the emission of pollen-tubes and their entrance into the 

 stigma. 



The structure and development of the ovules that are produced 

 within the ovary at the base of the pistil, and the operation in which 

 their fertilisation essentially consists, are subjects of investigation 

 which ha.ve a peculiar interest for scientific botanists, but which, in 

 consequence of the special difficulties that attend the inquiry, are 

 not commonly regarded as within the province of ordinary micro- 

 x-'tpists. Some general instructions, however, may prove useful to 

 such as would like to inform themselves as to the mode in which the 

 generative function is performed in phanerogams. In tracing the 

 origin and early history of the ovule, very thin sections should be made 

 through the flower-bud, both vertically and transversely ; but when 

 the ovule i.x large and distinct enough to be separately examined, it 

 should be placed on the thumb-nail of the left hand, and very thin 



1 It sometimes happens that when the pollen of pines or firs is set free, large 

 quantities of it are carried by the wind to a great distance from the woods and 

 plantations in which it has been produced, and are deposited as a fine yellow dust, 

 so strongly resembling sulphur as to be easily mistaken for it. This (supposed) 

 j> Mi-nil diffusion of sulphur (such as occurred in the neighbourhood of Windsor 

 in 1x791 has frightened ignorant rustics into the belief that the ' end of the world ' 

 was at hand. Its true nature is at once revealed by placing a few grains of it under 

 tin- microscope. 



