30 INTRODUCTION TO EMBRYOLOGY OF ANGIOSPERMS 



In a few plants a hypodermal archesporium has not been clearly 

 distinguished and more deep-seated cells are said to give rise to the 

 sporogenous tissue. In Doryanthes (Newman, 1928), Pholisma 

 (Copeland, 1935), and Holoptelea (Capoor, 19376) it is stated that 

 there is no definite system of periclinal divisions separating the 

 parietal tissue from the archesporium and that the sporogenous 

 function is gradually taken over by a group of cells about three or 

 four layers below the epidermis. It is probable, however, that such 

 appearances are due to the difficulty of obtaining a sharp differen- 

 tiation between the cells during the early stages of development of 

 the anther, and further studies may reveal the hypodermal origin 

 of the archesporium in these plants also. 



The Wall Layers. The epidermis, which is the outermost layer 

 of the anther, undergoes only anticlinal divisions. Its cells become 

 greatly stretched and flattened in order to keep pace with the en- 

 largement of the anther, and in many plants, especially those of dry 

 habitats, they eventually lose contact with each other so that only 

 their withering remains can be seen at maturity. 



The layer of cells lying immediately beneath the epidermis is the 

 endothecium. Its maximum development is attained at the time 

 when the pollen grains are about to be shed (Fig. 23). The cells 

 become radially elongated, and from their inner tangential walls 

 fibrous bands run upward, ending near the outer wall of each cell. 

 In aquatics with aerial flowers like Utricularia (Kausik, 1938) and 

 even such reduced forms as Wolffia (Gupta, 1935) the fibrous thick- 

 enings occur as usual, but in several members of the Hydrocharita- 

 ceae (Ernst-Schwarzenbach, 1945; Maheshwari and Johri, 1950), 

 and in some cleistogamous forms whose flowers never open, they 

 fail to develop and there is no special mode of dehiscence. In those 

 plants, also, whose anthers open by apical pores, the endothecium 

 may not develop any fibrous thickenings and dehiscence takes place 

 here by the dissolution of certain cells at the apex of the anther. 

 In Erica, which is an example of this kind, there is a further pecu- 

 liarity in that the "apical" pores are in fact basal. Figure 25 shows 

 some stages in the curvature of the anther which bring about this 

 inversion (Matthews and Taylor, 1926). 



Among other exceptions may be cited Musa (Juliano and Alcala, 

 1933), Sesamum (Nohara, 1934), Anona (Juliano, 1935a), Ipomoea, 

 (Juliano, 19356), Aeginetia (Juliano, 1935c), and Melastoma (Subra- 



