306 



PEACTICAL BOTANY 





Fig. 252. Diagram of part of a seed cone of 

 a pine, with ovules in normal position 



S, sporophylls, or leaf-like parts of the cone ; 0, 

 ovule (megasporangium) ; /, the covering of the 

 ovule, called the integument ; FG, the female 

 gametophyte,whichbearsthearchegoniumyl,in 

 which the egg is formed ; Ft, pollen tubes from 

 pollen grains which lie upon the tip of the ovule 



depends. All sorts of useful and 

 ornamental manufactured prod- 

 ucts depend upon these timbers, 

 and it is not easy to overestimate 

 their value to mankind. 



283. Asexual reproduction. Two 

 kinds of cones are borne upon a 

 pine plant. One is the seed cone 

 (Fig. 251) and the other is the 

 staminate cone. An examination 

 of a young seed cone will at once 

 show structures somewhat sim- 

 ilar to those of Lycopodium and 

 Selaginella. The cone 

 is composed of leaf-like 

 structures, on the up- 

 per sides of which ovules 

 (megasporangia) (Fig. 

 252) are borne. In the 

 ovules large cells, the 

 megaspores, are formed, 

 but one in each mega- 

 sporangium. The spore 

 does not escape from 

 this megasporangium. 

 Before relationships be- 

 tween spermatophytes 

 and pteridophytes were 

 known, the megasporan- 

 gium was always called 

 an ovule, a name which 

 is still largely used. 



The staminate cones 

 bear the microsporo- 

 phylls or stamens (Fig. 

 253), upon which are 



