THE HIGHER CRYPTOGAMIA. 221 



under the bud of the stem. But in consequence of the 

 subsequent growth in length and thickness of the interior 

 of the stem, the other axile bundle, and still more the cor- 

 tical bundles, are bent strongly inwards towards the longi- 

 tudinal axis of the stem as long as their course passes 

 within the prematurely developed peripheral tissue. This 

 bending usually amounts to 99° in the cortical bundles 

 (PI. XXX, fig. 4 ; PI. XXXI, fig. 1). A transverse section 

 passing through, or just over, the apex of the bud, exhibits 

 the vascular bundles which run almost horizontally to the 

 apex, in the form of from six to eight light streaks united 

 in a stellate manner. 



Soon after the appearance of thickening layers in those 

 cells of the axile bundles which have become widened into 

 scalariform vessels, there ensues such a considerable growth 

 of the cells of the interior of the stem, that the dispropor- 

 tion of the latter to the peripheral cellular layers disappears. 

 The bent portion of the cortical vascular bundles takes a 

 straight course ; the height of the axile cells becomes 

 almost equal to that of the cortical cells of the same age ; 

 which latter cells had far outstripped the former in 

 development, especially in the thickening of the cell- 

 membrane, as is perceptible in the peripheral vas- 

 cular bundles. As the growth of the interior of the 

 stem (by means of the extension of its cells) surpasses 

 that of the bark, which was prematurely developed by more 

 vigorous cell-multiplication, the cells of the interior are 

 three or four times longer than the peripheral cells. The 

 process may be considered as a pushing outwards of the 

 funnel-shaped depression around the terminal bud. It 

 occurs in like manner in Isoetes, Cycas, Mamillaria and 

 elsewhere, but much less distinctly on account of the close 

 crowding together, of the appendicular organs. 



The formation of new fronds always takes place above 

 the point of origin of the youngest scales. At some dis- 

 tance from the top cell of the apex of the stem, and sepa- 

 rated from the latter by from three to six cells, the mother- 

 cell of the frond is first visible in the form of a slight 

 elevation above the flat conical surface of the bud (PL XXXI, 

 fig. 3). The first step in the formation of a frond however 



