GROUPS OF PLANTS. 



75 



owing- to unequal tension, the sacs are ruptured longitudinally 

 and the spores scattered. The microspores are very numerous, 

 sometimes forming powdery deposits. They are either i -celled 

 or 3-celled. In the latter case two lateral cells act as wings for 

 the dispersal of the spores by the wind (Fig. 48, D). 



The Megasporophylls consist of sessile carpels (leaves) 

 on which are borne one or two naked ovules containing the spor- 



nc 



Fig 49. Longitudinal section of an ovule of a spruce (Picea): i, integument; no 

 nucellus (megasporangium) ; e, embryo-sac (megaspore) which has developed the female 

 gametophyte consisting of endosperm (e), two archegonia (a), which show the neck (c), 

 and the egg (n) ; p, germinating pollen grains (microspores) with pollen tubes (t) which 

 have penetrated the nucellus (nc) and reached the neck cells of the archegonia. After 

 Schimper. 



angia (nucelli). In certain groups, as in the pines, balsams, etc., 

 a scale is formed at the base of the carpel which bears the ovules, 

 and this scale is called the seminiferous scale. The ovules con- 

 sist of several parts (Figs. 49 and 50) : a stalk; an integument or 

 wall which has an opening at the apex known as the micropyle; 



