QYMNOSPEBM^. 



401 



the female flower of the Gymnosporms. The only consider- 

 able departure from the plan of the flower, as here given, is 

 found in the order Gnetacem, which will be described further 



on. 



510. — The ovule is at first a minute protuberance of 



em 



Pig. 297.-4, longitudinal section of an ovule of Pinua Larico, taken from a 

 cone just opened ; c, tlie coat of the ovule, in section ; o», the body or " nucleus" of 

 the ovule ; this includes all the figure which is filled out, showing the cells ; em, the 

 young embryo sac, £, a similar section of the ovule of Abiea peeiinata, after the en- 

 trance of the pollen tubes, pt. Into the corpupcula, cp, ep ; ov, the body or " nucleus'' 

 of the ovule— the upper portion is cut away (the cells composing its tissue are not 

 shown); w, the wall of the embryo sac; en, endosperm in the enlarged embryo sac ; 

 <», cp, two corpuscnlii ; ra, the neck of one of the corpuscula ; pr, the first cells of 

 the pro-embryo. A XISO; 3 X 30.— A after Hofmeister ; 3 after Strasburger. 



small-celled tissue ; a little later a ring gi-ows out from its 

 base, and rises as a sheath (the integument or coat), which 

 finally more or less completely closes it in ; in a few cases a 

 second integument forms outside of the first one. At a cer- 

 tain stage of its growth one of the interior cells of the ovule 

 grows larger than the others, and becomes the embryo sac 

 {em. Pig. 397, A) ; in it there arise numbers of free cells. 



