514 PINUS 



have a very stout epidermis with a hypoderm of thick walled tissue 

 under it, and the stomata are placed at the bottom of deep pits ; the 

 intercellular spaces too are veiy small. 



The fls. take the form ol the familiar cones, the 3 grouped together 

 in spikes. Each fl., whether 3 or ? , occupies the position of a short 

 shoot and is of limited growth an axis with a few scale-1. below bear- 

 ing a number of sporophylls. In the <? there are many sta., each with 

 two pollen-sacs on the under side; the pollen is loose and powdery, 

 and each grain has two bladdery expansions of the cuticle helping it 

 to float in the air. In the ? , the cpls. are very small, but the ovuliferous 

 scales, which show at the outside of the cone, are very large, and each 

 bears two ovules at its base, with the micropyles facing the axis. The 

 ? cones take 2 to 3 years belore the seeds are ripe. In May of the 

 first year, the lirst stage may be seen young cones, about i cm. long, 

 in the position of short shoots near the tip of the lengthening axis. 

 The ovules are not ripe for fert. In June (the time varies from year 

 to year according to season) pollination takes place. The i cones shed 

 their pollen in great quantities, so that in a pine forest the air is often 

 full ot it (if it rain, the phenomenon of 'showers of sulphur' may occur), 

 and the wind carries it about. At the same time the ovuliferous scales 

 spread apart. If a grain lall between two ol them it slips down to the 

 micropyle of an ovule, where it becomes held by the sticky fluid then 

 exuding. After a short time the ? cones close up again. The pollen 

 grain is brought into contact with the nucellus by the drying up of the 

 mucilage ; it forms a short pollen-tube, and then a resting period comes 

 on. Next year in May or J une the ? cone has become a fat green body 

 about 3 cm. long, with the ovules ready for fert. ; the pollen-tubes now 

 recommence growth and reach the ova. Then in the third year the 

 cone is matiue a hard woody cone containing the seeds between the 

 scales, Each seed contains an embryo with a whorl of cots., embedded 

 in rich endosp., and has a hard testa. To the end of this is attached 

 a thin membranous wing, derived from the ovulilerous scale. In dry 

 weather the cone opens and the seeds are blown away. In germ, the 

 seed is lifted up above the earth by the growing plant and the cots, 

 remain inside the testa till the reserves are exhausted. They are green 

 whilst in the seed, though in darkness an exception to the rule that 

 chlorophyll requires light for its formation. During the first year no 

 short shoots are formed, and the seedling has green 1. borne directly 

 on the main stem. 



The pines are amongst the most valuable of all plants and are 

 cultivated on an enormous scale, chiefly for their timber, which is 

 easily worked, and resinous products. The resin renders the timber 

 very resistent to decay, &c. Some of the more important sp. will 

 now be mentioned. (Cf. also under Pine.) 

 I. PINASTER Endl. Visible part of fruit scale more or less 



pyramidal with central boss. 



I. Pmea (short shoot with i or rarely i needles): 20 sp. 

 P. sylvestris L., the Scotch fir, the only Brit, sp., occurs 

 in Eur. to 68 N., in Asia to 66 N., and as far south as 

 Spain and Italy (alpine). The wood (yellow deal) is largely 

 used in the arts; turpentine is obtained by tapping the tree. 



