226 H0FME1STER, ON 



to the stem. They originate from the multiplication of one 

 of the cells of the free outer surface of the very young 

 frond, and are situated on its back or at the edges,* they 

 occur long before the first rudiment of the vascidar bundles 

 separates itself from the rest of the tissue (PL XXXII, 

 fig. 2). The divisions of the primary cell of the new shoot 

 follow the same rule as those of the apical cell of the 

 mother-axis. When the development of the bud goes on 

 slowly, the cortical tissue closes almost entirely over it 

 (PL XXXII, fig. 3). An accurate observer however may 

 even then discover the passage leading to the punctum 

 vegetationis, which is merely stopped up by entangled and 

 agglutinated scales (PL XXXII, fig. 3 4 ) : the passage is 

 blocked up by the drying of a portion of the mucilage, 

 which these buds of Pteris aquilina secrete in abundance. 



Aspidium filix-mas. The rudimentary and apical cells of 

 the first, and of all the succeeding fronds of this fern, divide 

 by means of septa inclined to the edges of the frond alternately 

 to the right and to the left ; the line in which each new sep- 

 tum cuts the next older one, is radial to the axis of the stem. 

 As far as can be gathered from the result of numerous 

 observations, the first septum which appears in the cell of 

 the first degree, is inclined to the left,f and turned towards 

 the next older frond (PL XXVI, fig. 14). This form of 

 division continues until the completion of the rudiment of 

 the stipes. When the formation of the blade of the frond 

 commences, septa make their appearance in the cell of the 

 first degree, and in the cell next to it of the second degree, 

 which septa are inclined alternately towards the front and 

 the hind surface of the frond. Thus the arrangement of 

 the cells in the growing portions of the frond is coincident 



_ * Upon the supposition of the adventitious bud being produced by the mul- 

 tiplication of a cell in the interior of the tissue, for instance, a cambial cell of 

 a vascular bundle, the gemmae of ferns would not be adventitious buds. But 

 this definition is too narrow, and could not be employed in many of the instances 

 which occur in phsenogams. 



f Following Braun's rule (' N. A. A. C. L.,' xv, p. 220,) of using the ex- 

 pressions right and left with reference to the direction of the development of 

 the organic body in question, I call that margin of the frond the right margin 

 which would be on the right hand of the observer, supposing him to be 

 placed in the longitudinal axis of the frond, with his face to the upper surface. 

 This margin of the frond is the front margin, turned towards the ascending 

 leaf spiral. 



