536 



G YMNOSPERMAE 



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

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

 known as * sulphur showers.' 



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

 *Ult. OSS./ II, 1870), which catches the pollen-grains brought by the wind and drawi 

 them into the micropyle as it dries up. 



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

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

 the pollen-tubes to penetrate the nucellar tissue. In Taxineae the pollen-grainsj 

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

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

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

 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 ovuliferous scale, in LarL 

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

 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 th 

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

 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 

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

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

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

 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 inconspicuoui 

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

 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 

 been observed. 



In angiospermous plants, Strasburger continues, the colouring of the perianth i| 

 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 

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

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

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

 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 furthe^ 

 evolved as the result of insect pollination later on. 



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

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

 description of the methods of fertilization in his memoir ' D. Befrucht. d. Coniferen,1 

 Jena, 1869. 



