284 



KNOWLEDGE. 



[Decembeb 1, 1898. 



The only question remaining is whether this series of 

 comparisons is supported by observations on the subsequent 

 history of the different parts. 



When one of the pollen-grains, which are blown in 

 countless numbers round the cones, comes to rest at the 

 micropyle of an ovule it adheres there owing to the presence 

 of mucilaginous material at the apex of the nucellus, and 

 its activity commences. While the small cell which we 

 regarded as representing a rudimentary prothallus remains 

 passive, the other throws out a tube which grows down 

 through the nucellar tissue toward the archegonium. The 

 protoplasm passes down with the growing tube, and finally, 

 when the latter reaches the archegonium, the active nucleus 

 of the microspore passes into the protoplasm of the egg- 

 cell, fuses with its nucleus, and thus forms the compound 

 nucleus from which the new plant subsequently arises. 



We may, then, regard our comparison between the 

 embryo-sac and pollen-grain of the pine with the Macro- 

 spore and Microspore of Selor/ineUa as proved, and we see 

 that in spite of the great gulf between Cryptogams and 

 Phanerogams we can still trace the con- 

 tinuity of the organs and processes of repro- 

 duction.'' 



VIII.-LILIUM. 



In conclusion, it will be our work to ex- 

 amine the corresponding parts of a typical 

 flower and see if we can carry the series of 

 comparisons yet a step further and bring the 

 highest representatives of plant life into line 

 with their lower and earlier relatives. 



The one chosen for illustration here is the 

 Mountain Lily {Lilium marta(jon). The speci- 

 mens were collected in July, at a height of 

 between six thousand and seven thousand feet 

 in the Eastern Alps, and the moth is drawn 

 from a specimen taken in the same locality, 

 though not actually seen visiting the flower. 



We noted that the Pine belonged to the 

 Gymwisperms or naked-seeded plants, because 

 the ovules and seeds are carried on the free 

 surface of scales and not enclosed in a special 

 case. The Lily, on the other hand, belongs 

 to the Awjiosperms, because the ovules and 

 seeds are contained within the walls of an 

 enclosing "ovary." It is, however, the posses- 

 sion of a "flower" which one naturally regards 

 as the distinctive feature of the Angiosperms, 

 and we have to ask at once, what is a flower, 

 and what parts of it, if any, correspond with 

 the structures we have seen in the Pine or in 

 Selaginella ? 



We may regard a flower as a shortened 

 axis bearing whorls (or spirals) of leaves, the 

 upper of which are modified in connection 

 with the essential organs of reproduction, 

 and the lower specialized for purposes accessory 

 to the process. If we imagine a pine cone short- 

 ened, its upperscales bearing ovules, those below 

 pollen-sacs, and the lowest become barren, 

 expanded, soft, and green or coloured, we 

 should have (details apart) the structural 

 plan of a flower. It would be impossible to say why the 

 lower leaves should become so altered if we knew nothing 



of the relationship between flowers and insects. Though 

 almost everyone has now a general idea of the important 

 part played by insects in securing the cross-fertilization of 

 plants, yet few recognize that the attraction of insects is, 

 biologically speaking, the reason for the very existence of 

 true flowers. The pine tree casts its myriad spores to the 

 wind and has no need of petals to its cones, and in the 

 same way the wind-fertilized angiosperms bear small and 

 inconspicuous flowers without a coloured perianth. Fer- 

 tilization by this method is uncertain, and an immense 

 amount of pollen has to be produced. With the greater 

 certainty attainable through the agency of insects there is 

 greater economy, but the plant must make its flowers 

 attractive, and often form those curious devices and traps 

 to make the insect do its work, the study of which forms 

 so fascinating a chapter in biological study. In our 

 mountain lily the plant's assistant seems to be usually 

 a day-flying moth, Macroglossa slellutarum, known in 

 Switzerland as the " Taubenschwanz " or "pigeon-tail." 

 There are nectaries or honey-glands at the base of the 



* The recent discovery that in some Cvcads and in the " Gingko " 

 (" Maidenhair tree ") the contents of the pollen tube actually form 

 ciliated motile spermatozoids, is of the greatest value in bridging this 

 gulf, and one of the most striking results of detailed microscopic 

 study. 



A. ^Flower of Lilium martagon (drawn from a specimen collected in July 

 near Davos Platz). B. — Median vertical section of the same, showing (a) tliree 

 of the Perianth Leaves ; (4) three of the Microsporop/iylls (stamens) ; {<■) the 

 three united Macrosporoph_i/lU (carpels), constituting the ovary in the centre, 

 prolonged above as the style with its terminal stigma. Growing on the central 

 axis of the ovary are the rows of Macrosporangia (oi-ules). c. — Macroglossa 

 sieUalarum, the Moth which effects the cross-fertilization of the plant (drawn 

 from a specimen taken in the same locality). D. — Transverse section of the 

 Microsporangium (anther), with Microspores (pollen-grains) developing in the 

 four chambers. E. and F. — Microspores (poUen-grains) at rest and in ger- 

 mination ; in F observe the presence of three nuclei. G. — Transverse section of 

 the Ovary, showing the Macrosporangia (ovules) growing from the central axis 

 formed by infolding of the edges of the Macrosporophylls (carpels). H. — A 

 longitudinal section of aMacrosporangium (ovule), showing the two coats separated 

 at the apex to form the Micropule, the central tissue of tlie Nucellus, and the 

 Macrospore (embryo-sac) enclosed in it. In the latter are seen, at the lower 

 (apical) end, the egg-cell with its two synergids (the group representing an arche- 

 gonium) ; in the centre the nucleus of the embryo-sac, and at the opposite pole 

 the antipodal cells. I. J. — The end of the pollen-tube comirvg in contact with the 

 egg-cell, showing the fusion of the sperm-nucleus of the former with the germ- 

 nucleus of the egg-cell, [i J, after Strasburger. The rest original.] 



perianth, and a long fold or half-closed tube leads to them 

 along the middle of the petals. The moth, hovering below 

 the flower, has to pass its long tongue down this tube in 

 its efforts to get at the honey, and in doing so becomes 

 dusted over by the shaking anthers above with the pollen, 

 which it afterward carries to another flower. 



We must, however, put aside the moth and the petals 



