520 A TEXTBOOK OF BOTANY [Cn. XIII 



(Taxus) having berries, and some others, diversely con- 

 stituted, in foreign parts. Some 350 species are known, 

 living mostly in cold temperate or mountainous regions, 

 where often they form great forests, the source of our most 

 valuable timber trees. 



The prevailing form is excurrent, with branches over- 

 lapping in a cone shape, giving a form specially fitted to the 

 snows they have to endure (page 179; Fig. 122). The leaves 

 are mostly evergreen (the Larch being a notable exception), 

 linear, or scale-like in form (pages 63-4), and xerophytic in 

 structure ; and thereby those plants are fitted to endure the 

 dryness of winter, when they are unable to absorb water 

 from the cold or frozen soil (pages 258-9). The xerophytic 

 character thus determined enables them to live in other dry 

 places, notably ridges and hills where they largely prevail, 

 though many (e.g. Arbor Vitse) can also stand plenty of 

 water, and even .thrive in swamps. Some of them, notably 

 Pines and Larches, produce two kinds of branches, the 

 ordinary long kinds, and others so short that the leaves are 

 brought together in rosettes or clusters familiar in the fascicles 

 of five in the White Pine. The wood is composed almost 

 wholly from tracheids (page 146), to which fact is due that 

 uniformity of grain which gives them their value as work- 

 able timber, and also as wood pulp for the making of paper. 

 Many kinds produce much resin, which waterproofs their 

 buds, keeps water from lodging among their leaves, and 

 resists entrance of Fungi when their soft wood becomes 

 broken. 



The reproduction in Conifers is wholly sexual. In typical 

 cases (Fig. 366), the staminate flowers, which form compact 

 cones at the base of the season's growth, are composed of 

 sporophylls, each of which bears on the under side two 

 microeporangia (the anther), containing many microspores 

 (pollen grains). These microspores, which often are pro- 

 vided with air sacs, making them easily carried by the wind, 

 germinate internally and produce one or two prothallial 



