476 IVansactions of. the Society. 



instance, the pollen-grain reaches the female cone more than a year 

 l)efore fertilization takes place. The nucleus divides into several 

 Ijodies, which pass along the pollen-tube and through an orifice 

 at the end enter the oosphere. Together with them much of 

 the protoplasm of the pollen-tube passes into the oosphere.* One 

 of these nuclei unites with the nucleus of the ovule, which it thus 

 fertilizes. What happens to the others, and whether one pollen- 

 grain can fertilize more than one ovule, does not yet seem clearly de- 

 termined. The account given by Belayff differs from that of Dixon. 

 According to him the pollen-grain contains three cells : the large 

 cell which grows out to form the pollen-tube, a small stalk-cell, 

 and a " body-cell," which divides into two cells which contain the 

 male sexual nuclei. It is not, however, clear from their description 

 what becomes of the nuclei of the pollen-chamber. 



A single pollen-grain may emit more than one pollen-tube, and 

 even if the tube is at first single it sometimes branches. Stras- 



* Dixon, Fertilization of Pinus. Ann. of Bot., 1894, p. 27. 



EXPLANATION OF PLATES VII. and Ylll.— continued. 



Fig. 51. — Lonicera Periclymenum Linn, x 400. Side view of pollen, showing 

 the face of one of the ridges, and the shallow furrow, SF, along the 

 middle of it. 



,, 52. — Ditto. End view of pollen, showing three wide depressions, DDD, and 

 which are three very wide furrows in the side view ; SF, SF, SF, 

 three shallow furrows on the outer face or edge of the ridges. 



,, 53. — Centaurea nigra Linn. Upper part of style x 20 ; AO, apex of anther- 

 cylinder ; BH, brush of hairs that pushes out the pollen from the 

 anther-cylinder; SA, side view of style arms ; P, pollen on the stig- 

 matic face. 



,, 54. — Ditto. Tip of the style arm x 80. 



,, 55 — Bellis j^o'ennis Ijinu. Pollen grain x 400. 



,, 56. — Mcrtensia cchioides Benth. x 800. Side view of pollen, showing two- 

 longitudinal furrows, with a pollen-tube, PT just protruding from one. 



,, 57. — Ditto. End view of pollen. 



,, 58. — Ditto. Pollen in water, showing the shape the furrows assume when 

 distended by the water ; PT, pollen-tube protuding from one of the 

 two furrows in view. 



,, 59. — Calamintha Acinos. x 400. Side view of pollen ; BR, BR, broad 

 ridges, corresponding to BR, BR in Fig. 61 ; AA, shallow furrows, 

 corresponding to AA in Figs. 60 and 61. 



„ 60. — Ditto. Edge view, showing two lateral shallow furrows, AA. 



,, 61. — Ditto. End view, showing two shallow furrows. A, and one broad and 

 deep furrow on each face, BF ; also two broad ridges, BR, BR, and 

 two narrow ridges, NR, on each face. 



,, 62. — Ulvius campcstris Linn, x 400. Pollen-grain, showing a pattern of 

 ridges on the flat face. 



„ 63. — Ditto. Pollen-grain, showing another pattern. 



,, 64. — Ditto. Pollen-grain, showing the depth on the edge, E. 



,, 65. — Juniperus nana Willd. Pollen-grain, showing six facets round a central 

 one. 



,, 66. — Luzula multiflora DC. var. congesta. x 400. Pollen-grain ; F, F, F, 

 framework of ridges, arranged tripodially ; TW, TW, TW, thin-walled 

 areas where shrinking or depression takes place. 



