366 Johnson : Development of Saururus cernuus L 



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The stamen has four pollen-sacs, each with a many-celled 

 archesporium, the wall and tapetum being formed in the usual 

 way. The pollen grains are shed soon after the definitive macro- 

 spore of the same flower is formed. They are then binucleate and 

 have a large thick area in the wall on one side. Nothing has been 

 seen as yet of the sprouting of the pollen grain or the mature pol- 

 len tube. Further careful work will probably discover this, 

 • though it is certain that the pollen tube is much less prominent in 

 the tissue of the style than in the related genus Peperomia. 



Soon after the edges of the carpel meet and before they have 

 fused far above the base, a single ovule appears on the inner face 

 of each half of the carpel near the suture (oi\ Fig. 2). These 

 ovules are clearly lateral in origin and not, in any case seen, basal 

 as described by De Candolle. Neither was any case found of 

 a third or fourth ovule as described by Bentham and Hooker, 

 though the latter character may perhaps be variable like the inser- 

 tion of the flower noted above. 



The ovules are sessile, orthotropous and at first transverse. 

 They originate at about the same level, but very soon one pushes 

 above the other with the micropylar end upward, and elongates 

 parallel to the axis of the carpel until finally it fills practically the 

 whole cavity of the latter. The lower ovule may develop far 

 enough to form a ripe embryo-sac, but no case of fertilization of 

 this was seen, and in the later stages it is transverse and flattened 

 against the bottom of the cavity of the carpel by the erect upper 

 ovule (tie, Fig. 4). The latter develops to form the single seed of 

 the ripe fruit (Fig. 6). 



The archesporial cell is single and axial, though at first there 

 are often two or three cells equally near the axial position in the 

 nucellus. The primary archesporial cell divides to form a tapetal 

 cell and a definitive archesporium. The former gives rise to but 

 few cells (tp y Fig. 5), which do not thicken their walls as do the 

 tapetal cells of Peperomia. 



The definitive archesporial cell or macrospore mother cell 

 divides by mitosis into an upper and a lower cell, of which the upper 

 divides once more while the lower immediately develops into the 

 functional macrospore or embryo-sac mother cell, which pushes 

 downward into the nucellus and upward to destroy the two de- 

 generating macrospores above (es, des y Fig. 3). 





