Fig. 32. Grains of pollen of Gesneria bulbosa emitting their tubes, magnified

180 times.

The tube is of extreme tenuity, and may be withdrawn from the
Masses of granular matter may be seen

stigmatic tissue with great facility.

descending the tubes at irregular intervals.

Fig. S3. A grain of pollen of the same plant, with its tube magnified 500 times: this shows that the tube is an extension of the outer membrane of the grain of The granular matter is pollen, if the latter was coated by more than one. seen passing down the tubes, and quitting the grain of pollen, which finally becomes a transparent empty vesicle.

Fig. 34. Grain of pollen of Datura Stramonium, emitting its tube; after Brongniart: a, pollen-tube.

Fig. 35. Grain of pollen of Ipomoea hederacea, emitting its tube; after Brongniart: a, pollen tube.

Fig. 36. Mode in which the pollen acts upon the stigma in Enothera biennis: a a, pollen tubes; b b, tissue of the stigma into which these tubes penetrate; after Brongniart,

Fig. 37. Mode in which the pollen acts upon the stigma in Antirrhinum majus;

after Brongniart. The pollen sticks to the surface of the stigma, and the tubes plunge down between the utricles of cellular tissue, of which the stigma consists.

Fig. 38. A grain of pollen of the same plant with its tube, more highly magnified: a, the pollen tube.

PLATE V.

Fig. 1. Vertical section of the ovarium of Dictamnus albus: a, gynophorus, or elongated base of the ovarium; b, base of the style; c, cavity where the carpella have not united; d, cell; e, placenta, with ovula attached to it. Fig. 2. Transverse section of the same in a more advanced state, where the carpella are beginning to separate: a a, carpella; b, an ovulum cut through; c, placenta.

Fig. 3. Pistillum of Coriaria myrtifolia; consisting of five carpella, each bearing a single linear stigma, and collected round a common elevated axis, the base of which is seen at a.

Fig. 4. Ovarium of Lamium album: a, base of the style; b, carpella pressed together into a square concave body; c, fleshy lobed disk.

Fig. 5. Pistillum of Pinguicula vulgaris: a, ovarium; b, style; c, stigma, consisting of two very unequal lobes.

Fig. 6. A vertical section of the same: a, the central free placenta; b, ovula; c, point where the placenta is connected, before fertilisation, with the stigmatic tissue.

a,

Fig. 7. A perpendicular section of the pistillum of Vaccinium amœnum : inferior ovarium combined with the tube of the calyx; b, limb of the calyx; c, epigynous disk; d, placenta; e, ovula; ƒ, style; g, stigma. Fig. 8. A transverse section of the ovarium of Hydrophyllum canadense, showing its remarkable placentation; a, wall of the ovarium; b, left placenta; c, right placenta; e, one of their points of union, the other is seen on the opposite side; d, a fleshy secreting annular disk. In this case, two placenta grow up face to face from the base of the ovarium, and gradually unite at their edges (e), enclosing the ovula within the cavity they thus form; this is proved by Nemophila, in which the placentation is the same, except that the placentæ are always distinct from each other; one of these placentæ, the ovuliferous face turned towards the eye, is represented at fig. 8.

Fig. 9. A perpendicular section of the inferior ovarium of Thamnea uniflora ; after A. Brongniart: a, tube of the calyx; b, wall of the ovarium; c, epigynous disk; d, ovula collected round a columnar placenta.

Fig. 10. Transverse section of the ovarium of Viola tricolor, showing its parietal placentation: a, one of the three placentas.

Fig. 11. Stigma of the same plant, which is inflated and hollow, with an orifice obliquely situated at its apex.

Fig. 12. Bifid stigma of Chloanthes Stoechadis; after Ferdinand Bauer.

Fig. 13. Hairy apex of the style and stigma, with its indusium, of Brunonia australis; after Ferdinand Bauer: a, stigma; b, indusium.

Fig. 14. The same, divided perpendicularly; a, stigma; b, indusium.

Fig. 15. Stigma of Banksia coccinea, with a part of the style; after Ferdinand Bauer.

Fig. 16. The earliest state of the ovula of Cucumis Anguria; this, and the succeeding figures, to 25 inclusive, are after Mirbel.

Fig. 17. Three of these ovules in a more advanced state.

Fig. 18. An ovulum at the period when the apex of the nucleus (a) is just appearing through the primine. The foramen has already become oblique with respect to the apex of the ovulum.

Fig. 19. An ovulum of the same, at the period when the secundine is appearing through the foramen: a, nucleus; b, border of secundine; the nucleus is now more oblique than before.

Fig. 20. An ovulum of the same, at a subsequent period, but still long before the expansion of the flower; the several parts are more developed; the nucleus, which at first was terminal, has now become lateral, and is evidently turning towards the base of the ovulum: a, nucleus; b, border of secundine. Fig. 21. An ovulum of the same, after fertilisation. In the interval between this state and the last, the primine has grown over the secundine and nucleus; the apex of the latter has turned completely to the base of the ovulum; and the foramen is contracted into the little perforation at a.

Fig. 22. Ovulum of Euphorbia Lathyris, in a very young state, long before the expansion of the flower: a, kind of cap projecting from the wall of the ovarium, and into which the apex of the nucleus (b) is inserted; this hood finally closes over the foramen, into which it protrudes as the nucleus retreats; c, the primine; the secundine is a similar cap included within the primine.