MALE CONES AND MICROSPORANGIA 



345 



w^<^ 



(e.g. Scotch Fir and other species of Pinus). In Pinits the 

 male cones replace the dwarf -shoots (Fig, 200), but in other 

 cases (e.g. Larch) the latter bear leaves below the male cones. 



The axis of the male cone (Fig. 202, A) supports large numbers 

 of densely crowded inicrosporophylls (stamens), which mostly 

 have the form of 

 flattened scales, 

 whose upturned 

 overlapping 

 tips are alone 

 visible at the 

 surface. They 

 usually bear two 

 large micro- 

 sporangia (pollen 

 sacs) on their 

 under-surface 

 (Fig. 202,'&, ps.) 

 although there 

 are sometimes 

 several (e.g. Cii- 

 pr es siis). In 

 Taxus the sta- 

 mens are peltate 

 in form, with 

 several (5 to 9) 

 pollen sacs pen- 

 dant from the 

 lower side of the 

 lamina (Fig. 201, 

 d). In Arau- 

 caria also the 

 microsporophylls bear numerous (10 to 20) pollen sacs. 



The young microsporangia are provided with a wall of several 

 layers which encloses large numbers of spore mother-ceUs, each 

 dividing in the customary manner to form four microspores 

 (pollen grains). The pollen sacs usually dehisce by means of a 

 broad split, and the pollen is distributed bj^ the wind. In Pinus 

 and its allies the microspores develop a pair of blister-lU^e en- 



FiG. 200. — The Scotch Fir (Pinus sylvestris). On the 

 right a branch bearing two clusters of male cones ; 

 on the left a branch with two fertilised female 

 cones above, a mature cone from which the seeds 

 have been shed below, and a young, just pollinated, 

 cone at the extreme apex. On both branches the 

 dwarf -shoots of the previous season areseen below, 

 and young dwarf -shoots of the current year's 

 growth above. (From a photo by W. B. Johnson.) 



