370 



XXVII. REPRODUCTION OF GYMNOSPERMS. 



most Coniferae several such cells adjoin one another, and form 

 a characteristic cell-body projecting more or less deeply into the 

 pollen-grain. These internal structures in the pollen-grain of 

 Gymnosperms are to be looked upon as a reduced prothallium, 

 which in Pinus is reduced so far that only a single cell, besides 

 the generative cell, remains in the ripe pollen-grain. The pollen- 

 grain of Pinus has a double membrane, the outer, the exine (or 

 exospore), the inner the inline or (endospore). The exine is 

 cuticularised, and at two laterally-situated places has undergone 

 cleavage in order to form vesicles, which first contain fluid, but 

 when ripe are filled with air, and thus form these bladdery wing- 

 like appendages. 



Female Cone of Pinus sylvestris. The Scotch Fir is monoe- 

 cious, so that we find male and female flowers upon the same plant. 

 The female flowers form a cone, in which numerous ovules, 

 inserted upon scale-like structures, are found combined. The 



small cones, either singly or several 

 together, occupy the apex of twigs 

 of the same age as themselves. 

 They stand in the axils of bracts 

 just like those of the short shoots, 

 each with two needle leaves, in- 

 serted lower down on the axis ; 

 their position at the end of the 

 shoot corresponds, however, with 

 that of the normal twig-forming 

 prolongation. The small cones are 

 usually in the receptive state at 

 the end of May, and, though small, 

 are recognisable by their brown- 

 red colour. They are stalked, and 

 stand erect ; the stalk is covered 

 with brown scales. Here also 

 alcohol material treated with glyce- 

 rine can serve for study. If 



we bring pieces removed from the axis of the cone with the 

 scalpel under the simple microscope, and isolate them with 

 needles, we can see (Fig. 135), that in the axils of delicate 

 obovate bracts (6), somewhat fringed at their margin, arise scales 

 (fr) of similar form, but fleshy, smooth edged, provided on the 

 inner side with a central projecting rib (c). These are distin- 



m 



FIG. 135. Pinus sylvestris. Fruit- 

 scale f with its two ovules, s, and the 

 central rib, c. Behind is the bract, b. 

 Upon the ovule the integument has 

 grown out into two prolongations, m 

 <x7). 



