LECTURE XXII. 



WE have seen that Selaginella is in many ways' a connecting-link 

 between the Ferns and Seed Plants. The truth of this statement 

 will be much more fully recognised when a study of the structure 

 and life-history of some of the Seed Plants has been made. 



We will begin our study with the examination of the Scots Pine, 

 Pinus silvestris. This tree forms forests in northern European 

 countries, but is found scattered in mountainous parts of the 

 British Isles. Its stout woody stem, heavy branches and strong 

 roots form a great contrast to the corresponding parts in the 

 common Ferns. Its stem tapers from base to summit and at 

 intervals puts forth a number of branches all round it at the same 

 level. These branches support secondary branches. The second- 

 ary branches, however, emerge only on the sides of the primary 

 branches, so that the lateral branching systems have a dorsiventral 

 appearance. The slender ends of the stem and branches are 

 clothed with green leaves. Examination of these ends show that 

 they terminate with a bud and that they are covered over with 

 large numbers of small scale-like leaves arranged in spirals upon 

 their surfaces. In the axils of each of these scales is a tuft of two 

 green needle-shaped leaves. The bases of the two green leaves are 

 continuous with, and attached to, a very short shoot or branch 

 inserted in the angle, or axil, formed by the scale with the support- 

 ing stem. The attachment of the green leaves to the top of the 

 dwarf shoot is concealed by a number of diminutive scales which 

 are fixed round the base of the leaves close to the top of the dwarf 

 shoot. The dwarf shoot has a limited life only, and after produc- 

 ing its two green leaves it ceases to grow, and it is detached from 

 the stem and falls off after three or four years. While the greater 

 part of the slender terminations of the stem and its branches are 

 covered over with scales including dwarf shoots, larger buds like 

 that at the apex are formed in the axils of the scales at the base 

 of each season's growth. These grow out into long shoots and 

 are the origins of the groups of branches on the main stem. 

 Similarly a pair of large buds which produce branches are formed 



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