CONIFKkAK: TI1K S< < )T< I'INK 



52; 



cones. On other plants staminal cones arc borix The tamens, or im< ro« 

 sporophylls, bear numerous pollen-sacs (microspore oil their lower nil 



The pollen-grains (microspores) from these gain 

 direct access to the micropyle of the exposed 

 ovule, and form short pollen-tubes, \vln< b 

 have been found in Cycas and Zamia to dis- 

 charge motile spcrmatozoids as the fertilising 

 bodies into a liquid secreted by the nucellus 

 (Fig. 415). In many respects the living 

 Cycadales show points for comparison on the 

 one hand with the primitive Ferns, on the 

 other with the remaining Gymnospcrms. 

 But the feature which possesses the greatest 

 comparative interest is that the motile sper- 

 matozoid is retained by them as the means 

 of fertilisation. Ginkgo biloba, the only living 

 representative of the Ginkgoales, a family 

 well represented in the Jurassic Period, is 

 also fertilised by motile spcrmatozoids. The 

 existence of zoidiogamic fertilisation in two 

 families of ancient Seed-Plants still living, and so distinct as these, is held 

 as strong evidence of the origin of Seed-Plants from a Pteridophytic ancestry. 



Fig. 415. 

 End of pollen-tube of Zamia, a 

 Cycad. showing the proth.illi.il cell 

 (v), the sterile sister-cell ($), 

 the two spermatozoids. a, before 

 movement of the spermatozoids has 

 commenced, b, after beginning of 

 ciliary motion. ( x about 75.) (After 

 Webber, from Strasburger.) 



CONIFERALES. 



The Scots Pine. 



The leading class of living Gymnosperms is the Coniferales, so named 

 from the fruiting body with its hard woody scales, as seen in t lie- 

 ordinary Fir-cone. The vast forests of such Conifers, existing in 

 temperate and sub-arctic zones, are the sources of the supply of soft- 

 wood, wood-pulp, turpentine and pitch. In the native British Flora 

 the Gymnosperms are represented only by Conifers, such as Scots 

 Pine (Pinus sylvestris), the Yew (Taxus baccata), and the Juniper 

 (Juniperus communis) ; but many more arc familiar in cultivation 

 in shrubberies and woods. Over the world at large they include 

 a number of other forms, somewhat loosely related, but with 

 common features that indicate their primitive character. Among 

 them are some of the largest and oldest of living organisms, such 

 as the Big Trees of California (Sequoia, see Frontispiece). Another 

 well-known and peculiar form is the Monkey Puzzle (Araucaria 



imbricata) . 



The seed of the Scots Pine, and of other Conifers, produces on ger- 

 mination a seedling with a dominating main axis, winch grows upright, 

 and keeps as a rule its radial construction. Radiating groups of 



B.B. 2t 



