236 



♦ KNOWLEDGE ♦ 



[June 1, 1886. 



other hand, more complex in structure than the single seed- 

 leaf plants, because their bark, wood, and pith are clearly- 

 defined, as in the double seed-leaf plants. Theii- lowest 

 representatives comprise the cycads or palm-ferns, so called 

 from their resemblance to palms, for which, with their 

 crown of feathery leaves, they are often mistaken. Next 

 in order is the much more varied and widely distributed 

 conifer family, notably pines, firs and larches, and, lesser in 

 importance, cedars and cypresses. A still higher class, 

 various in its modes of growth, marks the transition to 

 angiosperms, the flowers of both having many features in 

 common. 



The single seed-leaf angiosperms have no visible separa- 

 tion of their w^oody stuff into bark, stem, and pith, and have 

 no rings of growth, the wood exhibiting an even surface, 

 dotted over with small dark points. Their leaves have 

 parallel veins or " nerves," as in the onion and tulip, and 

 the blossom-leaves, or petals, are grouped in threes or mul- 

 tiples of three. Among their sevei-al representatives we 

 may single out the lilies for their beauty and fragrance, and 

 the cereals for their value and importance, both classes being 

 in near connexion, since the gi-asses from which man has 

 developed wheat, barley, oats, rice, and maize are, in a 

 botanical sense, degenerate descendants of the lily family. 



The double seed-leaf plants include all the highest and 

 most specialised varieties. Bark, stem, pith, and concentric 

 rings of growth are clearly defined ; the leaves are netted- 

 veined, and the petals grouped in fours or fives or multiples 

 of tho.se numbers. The lowest class, represented by the 

 catkin-bearers, as the birch and alder, the poplar and the 

 oak ; and by plants allied to the nettle and to the laurel, are 

 nearly related to the highest gymnosperms. Next in order 

 are the crown-bearers, or flowers with corollas, as the rose 

 family, which includes most of our fruit-yielders, from 

 strawberries to apples ; while the highest and most perfect 

 of all are plants in which the petals are united together in 

 bell-shape or funnel fashion. Such are the convolvulus and 

 honeysuckle, the olive and ash, and, .at the top of the plant- 

 scale, the fiimily of which the daLsy is the most fiimiliar 

 representative. Its position among plants corresponds to 

 man's position among animals. As he, in virtue of being 

 the most complex and highly specialised, is at their head, 

 albeit many exceed him in bulk and strength, so is the daisy 

 with its allies, for like reasons, above the giants of the 

 forest. 



The primary function for which the organs of plants 

 known as flowers exist is not that which man has long 

 assumed. He once thought that the earth was the centre 

 of the universe, until astronomy dispelled the illusion, and 

 there yet lingers in him an old Adam of conceit that everj- 

 thinjj on the earth has for its sole end and aim his advantaije 

 and service. Evolution will dispel th.at illusion. But our 

 delight in the colours and perfumes of flowers will not be 

 lessened, while wonder will have larger field for play in 

 learning that the coloured leaves known as flowei-s, together 

 with their scent and honey, have be?n developed in fm-ther- 

 anoe of nature's supreme aim — the preservation and incr&ase 

 of the species. And truly the contrivances to secure this 

 which are manifest in plant-life are astounding, even to 

 those who perceive most clearly the unity of function which 

 connects the highest and lowest life-forms together. It is 

 diflicult, nay, well-nigh impossible, to deny the existence of 

 a rudimentary consciousness in the efl^orts of certain plants 

 to secure fertilisation. Take, for example, the well-known 

 aquatic plant, VaUisneria spiralis. When the male flowers 

 detach themselves and float about on the water, the female 

 flowers develop long spiral stalks by which to reach them, 

 and become fertilised by the discharge of pollen on their 

 pistils. Most flowers have their male and female organs 



within the same petals, and in .some ca.ses fertilise them- 

 selves by scattering the pollen from the bursting stamens 

 on the stigma or head of the pistil. But nature is op- 

 posed to this; ''tells us in the most emphatic manner that 

 she abhors perpetual self-fertilisation," with its resultant 

 puny and feeble offspring ; and we find a number of con- 

 trivances to jnevent this, and to .secure fertilisation by the 

 pollen of another plant, to the abiding gain all round of the 

 plant, whose blood, as we. may say, is thus mixed with that 

 of a stranger. Two agencies — insects and the wind — un- 

 designedly effect this ; while in the dispersion of the matured 

 seed, birds and other animals play an important, although 

 equally unconscious, part. 



Plants which are wind-fertilised have no gaily-coloured 

 petals or sepals, and do not secrete nectar. Such are the 

 naked-seeded groups whose sombre flowers are borne on dull 

 brown cones ; and, among cover-seeded gro\ips, grasses and 

 rushes with their feathery' flowers ; and willows and birches, 

 with their long waving clusters of catkins. All of these pro- 

 vide against the fitfulness of the wind, which is as likely to 

 blow the pollen one way as another, by producing it in large 

 quantities. 



Plants which are insect-fertilised seek to attract their 

 visitors by .secreting honey and developing coloured floral 

 organs. 'The way in which this came about is probably as 

 follows. 



The common idea about flowers is that they are made 

 up of petals and sepals, whereas the essential parts are the 

 stamens and pistils — i.e. the male, or pollen-producing 

 organs, and the female, or seed-containing organs. The 

 earliest flowers consisted of these alone, having no coloured 

 whorl of petals within another coloured whorl of sepals, 

 but were only scantily protected by leaves, as are many 

 extant species. These the food-seeking insects then, as now, 

 visited for the sake of the pollen, to the detriment of the 

 plant, which lost the fertilising stuft" and gained nothing in 

 I'eturn. To arrest this, certain plants began, especially when 

 in the act of flowering, to secrete honey and store it in glands 

 or nectaries, or near their seed-vessels, where the insects could 

 not get at it without covering then- bodies with some of the 

 pollen, wliich they rubbed on the pistils of the plant next 

 visited, and thus fertilised the ovule, provided that the plants 

 were nearly related. Honey is sweeter to the taste than pollen, 

 and the plants that produced the most honey stood the 

 better chance of visits from insects, and therefore of fertili- 

 sation, to the advantage of their species over others. As a 

 rule, those which secrete honey have hairy coverings at the 

 base of the petals, or other contrivances to prevent it being 

 washed out bj- the rain or dew, or seized by useless insects, 

 and we find curious interrelations established between plants 

 and their desired visitors. Certain flowers adapt themselves 

 to certain insects, and vice versil, as where the plant has 

 secreted the honey at the bottom of a long tube and the 

 insect has developed a correspondingly long proboscis to 

 gather it. By these and kindred devices the pollen is pre- 

 served for its sole function, the energy of the plant being 

 conserved in the smaller quantity which it has to produce. 

 As the honey w.as secreted as counter-attraction to the 

 pollen, so the coloured floral envelopes were developed to 

 attract the insects to the honey-secreting plant, and those 

 floral whorls, both of petals and sepals, are modified or 

 transformed stamens which have exchanged their function 

 of pollen-producers for that of insect-allurers. And as both 

 stamens and pistils are loaves aborted or modified for the 

 special function of reproduction, Goethe's well-known 

 generalisation that the leaf is the type of the plant has a 

 large measure of truth in it. 



But before speaking further about colour-development in 

 plants, it may be useful to say a little about colour itself. 



