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The archesponum is stated by some observers to give 

 off at its apex a parietal cell similar to that described for 

 the micro-sporangium archesporial cells. Coulter and 

 Chamberlain'^ state that a parietal cell is very generally 

 cut off in grasses, and that Koernicke and others find this 

 to be the case with wheat. My preparations do not 

 confirm this in the varieties examined, the nearest 

 approach thereto being the upper part of the apical 

 non-niiclcatc archesporial cytoplasm (Fig. i6), but no 

 dividing wall can be seen. Cannon describes Avena fatita 

 as being without a parietal cell. Further, Koernicke is 

 said to find a large development of " parietal " tissue 

 around the deep-seated embryo-sac ; this tissue, however, 

 appears to be derived from acti\c division of the 

 surrounding nucellus cells. In all stages from the first 

 division of the archesporium to the mature embryo-sac, 

 median sections always show the apex abutting directly 

 on to the epidermis of the nucellus. Outside, the four 

 layers of the two integuments closely press upon the 

 nucellus, practically closing the micropyle, and might 

 easily be mistaken for parietal tissue (Fig. 17). Transverse 

 sections of the ovule may be particularly misleading in 

 this respect. 



The transition of the archesporial cells into megaspore 

 mother-cells corresponds to the transition of micro- 

 sporogenous cells into microspore mother-cells. B)' two 

 successive mitoses tlie archesporium first becomes two 

 celled (Fig. 13), and then gives rise to a tetrad row of four 

 megaspore mother-cells separated from one another by- 

 distinct walls (Fig. 14), as figured' also by Koernicke^ in 

 his thesis on the sexual organs in wheat. No sooner does 

 the tetrad become evident than its upper three cells begin 

 to disintegrate and disappear, whilst the fourth, lowest and 

 innermost, nourished by their substance, enlarges greatly 



