178 



PLANT STRUCTURES 



the body of the sporangium (Fig. 148, d), and was at first 

 not recognized as being a spore. 



These structures had also received names before they 

 were identified with the corresponding structures of the 

 lower groups. The megasporophyll was called a carpel, 

 the megasporangia ovules, and the megaspore an embryo- 

 sac, because the young embryo was observed to develop 

 within it (Fig. 147, em). 



The strobilus of megasporophylls, therefore, may be 

 called the carpellate strobilus or carpellate cone. As the 

 carpel enters into the organization of a structure known as 

 the pistil, to be described later, the cone is often called 

 the pistillate cone. As the staminate cone is sometimes 

 wrongly called a "male cone," so the carpellate cone is 

 wrongly called a "female cone," the 

 old idea being that the carpel with 

 its ovules represented the female sex 

 organ. 



The structure of the megaspo- 

 rangium, or ovule, must be known. 

 The main body is the nucellus (Figs. 

 148, c, 149, nc) ; this sends out from 

 near its base an outer membrane 

 (integument) which is distinct above 

 (Figs. 148 #, 149 i), covering the main 

 part of the nucellus and projecting 

 beyond its apex as a prominent neck, 

 the passage through which to the apex 

 of the nucellus is called the micropyle 

 ("little gate") (Fig. 148, a). Cen- 

 trally placed within the body of the 

 nucellus is the conspicuous cavity 

 called the embryo-sac (Fig. 148, d), 

 in reality the retained megaspore. 

 The relations between integument, micropyle, nucellus, 

 and embryo-sac should be kept clearly in mind. In the 



FIG. 148. Diagram of the 

 carpel structures of pine, 

 showing the heavy scale 

 (A) which bears the 

 ovule (B), in which are 

 seen the micropyle (a), 

 integument (6), nucellus 

 (c), embryo sac or mega- 

 spore (d). MOORB. 



