GYMNOSPERMAE. CONIFERAE. 3 25 



the staminal leaf in Tax us baccata bears from three to eight (Fig. 252), in Juniperus 

 communis and most of the Cupressineae three roundish pollen-sacs (Fig. 253); 

 those of Abies, Pinus, and their allies lie in pairs parallel to or obliquely beside one 

 another beneath the peltate scale right and left along its stalk, which resembles the 

 connective of the Angiosperms ; in Araucaria and Dammar a on the other hand 

 the long cylindrical pollen-sacs hang down free in larger numbers. 



The pollen-sacs or microsporangia have special contrivances of different kinds 

 for their protection while they are still young. In Pinus, Abies, and other genera 

 they are more or less sunk like the sporangia of Ophioglossum in the tissue of the 

 sporophyll or staminal leaf; in Gingko they have a thick wall of several layers of cells; 

 in Cupressus, Thuja, and many species of Juniperus they are covered by a special 

 growth of the tissue on the under side of the staminal leaf, which then appears like a 

 continuation of the expanded portion of the stamen 1 . This formation is no doubt 

 analogous to the indusium of the sori of the Ferns, and may therefore be called 

 an indusium. A similar formation, mutatis mutandis, is also found in the leaves, 

 in the axils of which the macrosporangia are placed. 



The development of the microsporangia (pollen-sacs) agrees entirely, as far as it 

 is known, with that of the sporangia of Lycopodium, that is, the sporogenous tissue is 

 the product of an archesporium and is surrounded by tapetal cells. The microspores 

 (pollen-grains) are formed by division of the mother-cells into four daughter-cells. 



The usually delicate wall of the pollen-sacs at length bursts longitudinally and 

 releases the pollen-grains or microspores, which are produced in extraordinarily large 

 quantities, since they are dependent for the most part on the wind for conveyance to 

 the female organs of the same or of some other tree. The pollen-grains which 

 happen to fall on the orifice of the micropyle of the ovules are retained there by a 

 drop of liquid which issues from the micropyle ; this liquid fills the canal of the micro- 

 pyle at this time, but it afterwards dries up and so draws the captive pollen -grains 

 down to the nucellus, where they at once send in their tubes into its loose tissue. 

 This arrangement is sufficient in the Taxineae, Cupressineae and Podocarpeae, 

 where the micropyles project free to the outer air ; but in the Abietineae, where they 

 are more concealed among the seminiferous and bract-scales, these structures them- 

 selves form suitable canals and grooves at the time of pollination, by means of which 

 the pollen-grains are conducted to the micropyles 2 . The large number and lightness 

 of the pollen-grains is favourable to their transportation by the wind over considerable 

 distances ; in the true Pines and the Podocarpeae their buoyancy is still further aided 

 by the distension of the exine into hollow vesicles, represented in Fig. 255 IV, V. 



The formation of a rudimentary prothallium inside the pollen-grain takes place 

 in the Coniferae as in the Cycadeae (Fig. 248), and before pollination. The process 

 is very simple in Taxus, Podocarpus, the Cupressineae, Araucaria, and the true Pines,, 

 where the contents of the grain divide by a transverse wall into a large and a small 

 cell, the latter of which undergoes no further change (Fig. 255); in the rest of the 

 Abietineae the dividing wall bulges out into the space enclosed by the inline 

 (Fig. 255 /, //, ///); in this apparently unimportant fact we have another instance 



1 See Beitr. z. Vergl. Entwicklungsgeschichte d. Sporangien, II (Bot. Ztg. 1881). 



2 See Strasburger, loc. cit. on page 319. 



