32 MORPHOLOGY OF ANGIOSPERMS 



The development of the microsporangia began to be de- 

 scribed by Xa'geli 2 in 1842, and was continued by Hofmeister 3 

 in 1859-' 61 ; but the first detailed account from the standpoint 

 of modern morphology is that of Warming 8 in 1873, which has 

 been made the basis of all subsequent accounts. This was sup- 

 plemented in 1876 by Engler, 9 and since then numerous inves- 

 tigators have added extensively to the literature of the subject. 



The anther at first is a homogeneous mass of small meriste- 

 matic cells covered by an epidermis (Fig. 9). Very early it 



FIG. 9. Development of the microsporangium. A-D, Doronicum macrophyllum : A, 

 transverse section of very young anther, showing primary sporogenous cell (a) and 

 primary parietal cell (b) ; _Z?, slightly older stage ; 6 y , longitudinal section of anther in 

 same stage as that shown in B \ I), later stage ; a, sporogenous cells. E, Menyanthes 

 trifoliata, transverse section of a microsporangium at a still later stage showing 

 tapetum (t) and microspore mother-cells (sm). F, Mentha aquatica, transverse sec- 

 tion showing tapetum (t} and sporogenous cells (a). After WARMING, from Goebel's 

 Outlines of Classification and Special Morphology. 



becomes faintly four-lobed in cross-section, and the differentia- 

 tion of the vascular strand of the connective outlines the gen- 

 eral plan of the structure. The whole hypodermal layer of 

 cells, representing the outermost layer of the periblem, is prob- 

 ably to be regarded as archesporial in its possibilities, and one 

 region of it is just as likely as another, under similar condi- 

 tions, to develop into actual archesporial cells. The favorable 

 conditions for this development, however, are under the lobes ; 

 so that almost simultaneously with their appearance, a plate 



