THE CONIFERS 185 



tissue in the Pteridophytes, but much modified and 

 reduced. Here, then, within the ovule of Picea, we 

 have a genuine prothallus filling the embryo-sac (mega- 

 spore) and supporting archegonia. Each archegonium 

 has a neck of small cells, and a large basal cell called the 

 venter, a; the venter encloses the egg-cell, or ovum, o. 

 In these details we detect a marked similarity to the 

 structures arising in the megaspores of the higher 

 Cryptogams — a similarity so pronounced as to suggest 

 a cryptogamic origin for the Gymnosperms. 



It has been pointed out that a rudimentary prothallus 

 appears in the germinating pollen grain of the Gymno- 

 sperms (see p. 172) ; this is awanting in the Angiosperms. 

 In the latter we have reduction and specialization carried 

 to their culmination, but in the former the pollen grain 

 (microspore) is more complicated. 



The time elapsing between pollination and fertiliza- 

 tion in the Conifers is often greatly protracted; in 

 Picea excelsa, as already noted, it is about six weeks; 

 in the Scotch Fir, Pinus sylvestris (Plate X.), the seeds 

 take two years to ripen. 



The Coniferse are grouped in two families, the group- 

 ing being based on different points of floral structure. 

 First we have the Taxacece, of which the well-known 

 Common Yew, Taxus haccata, the only species found in 

 Britain, is a good representative; it is dispersed over 

 Europe, North and Central Asia, and North America. 

 The entire family comprises only about seventy species. 

 The Taxacese usually have female cones with but few 

 scales. The Common Yew is evergreen. Its leaves 

 are from \ to | inch long; they are narrow and flat. 

 The sexes are represented on different plants. The 



24 



