536 GYMNOSPERMAE 



during anthesis of the flowers in fir- or pine-woods it is often carried some distance 

 by the wind and when washed to the ground by rain produces the phenomenon 

 known as ' sulphur showers.' 



The micropyle of the ovule secretes a drop of fluid during anthesis (Delpino, 

 'Ult. OSS.,' II, 1870), which catches the pollen-grains brought by the wind and draws 

 them into the micropyle as it dries up. 



During pollination the apex of the nucellus becomes loosened, and usually 

 excavated, being thus prepared to receive the pollen-grains and to render it easy for 

 the pollen-tubes to penetrate the nucellar tissue. In Taxineae the pollen-grains, 

 driven by the wind, reach the ovules directly ; in Cupressineae they are partly guided 

 to the orthotropous ovules by the ovuliferous scales ; in Abietineae there are special 

 organs for guiding the pollen, and in Pinus sylvestris Z., P. Pumilio Haenke, and 

 Picea Link, the ovuliferous scales, and in Larix and Abies the carpels do this. 

 A keel situated, in the first two species named, on the ovuhferous scale, in Larix 

 Tourn. and Abies L. on the carpel, indicates the right way for the pollen-grains. In 

 Picea the keel is absent, but the scales are so formed that pollination is easily effected 

 without it (Strasburger). 



Each pollen-grain of some monoecious species possesses, as has been mentioned 

 above, two air-sacs, which render them very easy to move. Hartig (Bot. Ztg., 

 Leipzig, XXV, 1867) assumes that these occur in pines, firs, and spruces, because the 

 female flowers mature at the top of the tree very markedly in the two first and 

 predominantly in the last, and the air-sacs therefore help the pollen-grains to move 

 upwards and so reach the female flowers. This assumption does not, however, at all 

 explain the presence of air-sacs in species of Podocarpus Pers., Tsuga canadensis 

 Carr, and others. Strasburger is of opinion that the facility of motion imparted to 

 the pollen-grains of some species is attained by those of others in different ways, 

 i. e. by great dryness and special smallness of the grains. 



Strasburger points out another peculiarity of the cones : at the time of pollination 

 they are usually of a beautiful bright-red colour, and become later an inconspicuous 

 green or brown. Such colours are known to serve as attractions for insects in 

 angiospermous plants. Such a significance is, however, impossible for the colouring 

 of cones, as pollen is always removed by wind and transfer by insects has never yet 

 been observed. 



In angiospermous plants, Strasburger continues, the colouring of the perianth is 

 an inherited peculiarity which is useful for pollination. But what of the coloration 

 in Coniferae .? It cannot be an inherited peculiarity, for the Coniferae cannot be 

 derived from entomophilous plants. There is therefore no alternative but to take the 

 red colouring of the cones during anthesis as a coincidence called forth secondarily 

 by increased vitality at that time, and disappearing again later. We may suppose, 

 says Strasburger, that the analogous colouring of the perianth in angiospermous plants 

 also owes its origin to a similar cause, and was only found to be of value and further 

 evolved as the result of insect pollination later on. 



These last opinions I have extracted from Strasburger's memoir ' D. Bestaub. d. 

 Gymnospermen ' (Jenaische Zs. Natw., vi, 1871, pp. 249-61). He gives a detailed 

 description of the methods of fertilization in his memoir ' D. Befrucht. d. Coniferen,' 

 Jena, 1869. 



