Box— Vol. I.] CANNON— AVENA FATUA. 335 



considered to make up a perianth. They are homologous 

 to the perianthal lodiculse of the rye and cannot, therefore, 

 hold similar relations to the lodiculse of Avena. I conclude 

 then from a comparison of the grass flowers that the lodic- 

 ulae in Avena do not represent a perianth, but that the 

 perianth is entirely wanting; they are homologous to the 

 stipular lodiculae of other grasses. 



From this it would appear therefore that not all those 

 organs called lodiculae are necessarily or even probably the 

 same morphologically. In some grasses they are survivals 

 or rudiments of a perianth, in others they are survivals or 

 rudiments of extra-floral leaves, and in still others, where 

 two rows occur, the inner row is morphologically perianth, 

 the outer extra-floral bracts, and there is no evidence 

 (Eichler) of a double perianth. 



III. The Stamen. 



The development of the stamen of Avena, as far as fol- 

 lowed, corresponds rather closely with that of the stamen 

 of wheat, (Koernicke, 1896). The stamens originate as 

 crown-shaped projections at equal distances apart on the 

 periphery of the floral axis. A cross-section shows the 

 young stamen to be oblong in form (fig. 8). By more 

 rapid growth in the portions where the loculi are to appear, 

 the outline becomes irregular and characteristic of the 

 stamens of Angiosperms (fig. 9). A constriction occurs 

 very early at the base of the stamen, which indicates the 

 beginning of the filament (fig. 7). The subsequent growth 

 of the stamen until the time when the pollen grains are ripe 

 is due almost entirely to the elongation of the anthers — the 

 filament growing only immediately before the pollen is 

 scattered. The primary tissues — plerome, periblem, and 

 dermatogen — are clearly marked in the young stamen. As 

 usual in Angiosperms, the pollen is derived from the peri- 

 blem. In the increase in diameter of the anther, preceding 

 the cutting off of the archesporium, the cells of the periblem 

 in the parts where the loculi are to appear become larger 



