THE ANGIOSPERMAE 



1399 



built up between the epidermis and the archesporium, which thus comes to 

 be deeply embedded in the midst of the nucellus. Rosa and Alchemilla are 

 cases in point (Fig. 1297). 



Fig. 1297. — Salix glaucophylla. A, Single archesporial cell. B, Archesporial cell divided into 

 parietal cell and primary sporogenous cell. {After Chamberlain.) C, Rosa livida. Multi- 

 cellular archesporium lying beneath several layers of parietal cells formed by the 

 periclinal divisions of the primary parietal cell. The nucellar epidermis has also under- 

 gone several periclinal divisions. {After Strasburger .) 



Generally the separation of parietal cell and sporogenous cell implies a 

 functional differentiation, but instances are known in which the parietal 

 cell or cells produce accessory embryo sacs. This is particularly the case 

 in Malvaceae, in which most species have a rather massive development of 

 parietal tissue, as a rule seven to twelve cells thick. Several of these cells 

 may become accessory embryo sac mother cells, but only rarely is their 

 development completed. 



An attempt to reduce the varied conditions of archesporial development 

 into a classified order has been made by Schnarf, who recognizes six types. 



Type I. A number of sub-epidermal cells in the nucellus are differenti- 

 ated as archesporium. Each cell divides periclinally into a short row of cells, 

 the outer of which become parietal cells. The inner cells divide repeatedly 

 to form a complex of sporogenous cells. 



Type II. The first condition is as in Type I. Each archesporial cell 



M* 



