164 



Elementary Biology. 



the orthotropal, known as campylotropal. The sporangium 

 has usually two cellular coverings, the outer coat being 

 known as the ' primine,' the inner as the * secundine.' It 

 is preferable to discard these terms altogether and talk of 

 them simply as the outer and inner coats of the ovule. 

 The central tissue of the ovule is known as the ' nucellus, 

 sunk in the interior of which is found one ovospore, which 

 goes by the name of the ' embryo-sac.' If we study the deve- 

 lopment of the sporangia (male and female), we shall be able 

 to distinguish clearly the homologies of the several parts. 1 



FIG. 84. DIFFERENT POSITIONS OF OVULES. (Prantl.) 



A, orthotropal ; B, anatropal ; c, campylotropal ; a z, ii, coats of the ovule ; 

 A, nucellus; w, micropyle ; e i, embryo-sac ; f, funicle ; r, raphe. 



The development of the stamen. The stamen appears 

 first as a small prominence on the floral axis (or thalamus, 

 as it is sometimes called). Very early a division of the 

 prominence takes place, indicating the primary divisions into 

 two pairs of spermo sporangia. The tissue between the 



1 It is very unfortunate that the terminology of the reproductive 

 organs of the Angiospermce is so different from that of the lower plants. 

 The terms ovule, anther, ovary, and such like, have, however, become 

 by long usage so firmly associated with these structures that it is almost 

 impossible now to get rid of them. It is necessary, however, that the 

 student should in all cases know not only the terms in ordinary use, 

 but also the terms which are morphologically correct. In order to 

 familiarise the reader with either terminology, use will be made of both 

 series of names. 



