454 GYMNOSPERMS LESS. 



B, a single microspore, showing bladder-like processes of outer coat, 

 and contents divided into small prothallial cell (a) and large cell (b), 

 from which the pollen-tube arises. 



C, diagrammatic vertical section of female cone, showing axis with 

 female sporophylls (sp. ph. 9 ) bearing megasporangia (nig. spg), each of 

 which contains a single megaspore (nig. sp) : per, the scale-like perianth 

 leaves. 



D, diagrammatic vertical section of a megasporangium, showing 

 cellular coat (t), and nucellus (ncl), micropyle (mpy\ and megaspore 

 (mg. sp} : the latter contains the prothallus (prth) in which are two 

 ovaries, that to the left showing a large ovum (ov) and neck-cells, while 

 that to the right has given rise - to an embryo (emb) which is in the 

 phyllula stage, and has sunk into the tissue of the prothallus by the 

 elongation of the long suspensor (sfsr). 



A microspore (mi. sp) is seen in the micropyle sending off a pollen- 

 tube (p. /), the end of which is applied to the necks of the two ovaries. 



E, diagrammatic vertical section of a seed, showing coat (/), micro- 

 pyle (mpy), and endosperm (end), in which is imbedde I an embryo in 

 the phyllula stage, consisting of stem-rudiment (st), cotyledons (ct), and 

 root (r). 



(A and B, altered from Strasburger ; D and E, altered from Sachs. ) 



are borne on the same cone. In the pines and their allies 

 both male and female cones are usually borne on the same 

 tree, so that the plant is monoecious: many Gymnosperms, 

 on the other hand, are dioecious^ each tree bearing either 

 male or female cones only. 



The male cones (Fig. 119, A) are borne in clusters or 

 inflorescences near the distal ends of the branches. P^ach 

 cone consists, as in Equisetum and Selaginella, of an axis 

 bearing a large number of sporophylls (sp. ph. g ) : it springs 

 from the axil of a leaf and is to be looked upon as an 

 abbreviated and peculiarly modified shoot. 



The sporophylls or stamens as they are commonly called 

 (Figs. 119, sp.ph. and Fig. 120), are more or less leaf-like 

 structures, each consisting of a short stalk or filament and an 

 expanded portion or anther, the latter bearing on its under or 

 proximal side two microsporangia or pollen-sacs (mi. spg). 

 The mother-cells of these divide each into four microspores 

 or pollen-grains, which are liberated by the rupture of the 



