THE HIGHER CRYPTOGAMIA. 217 



of brown cells. It is this distribution of the tissue com- 

 posing the stipes which produces the well known figure of 

 the eagle seen on an oblique section. 



Delicate longitudinal sections through the terminal bud of 

 the stem of Pteris aquilina, exhibit with the greatest clear- 

 ness the transformation of the originally homogeneous 

 parenchymatal tissue into vessels and bast-cells. The in- 

 vestigation is very much facilitated by the course of the 

 inner one of the two primary vascular bundles, which is 

 straight and parallel to the axis. According as the section 

 is taken parallel to the surface of the earth, through the 

 longitudinal ridges of the creeping stem, or at right angles 

 to this direction, the wedge-shaped cell which encloses 

 the apex of the flatly conical deeply buried terminal bud 

 is seen either on its three-sided front aspect (PI. XXXI, 

 fig. 5), or its four-sided lateral aspect (PL XXXI, fig. 4). 

 The funnel-shaped depression, at the bottom of which the 

 terminal bud is seated, is strongly compressed from above 

 and below. The walls of the depression are thickly clothed 

 with scale-like hairs. The erect ends of the hairs, which 

 are closely pressed against one another, and fastened to- 

 gether by a hardened mucilage secreted from the bud, 

 entirely close the mouth of the funnel, and shut off the 

 delicate young portions at its base from the outer air. The 

 end of the stem in its longitudinal growth forces its way 

 through the toughest clay, without injury to the delicate bud 

 buried in its apex. 



The clearly defined mode of arrangement of the cells of 

 the second degree, and of their derivatives, affords an im- 

 mediate explanation of the deep depression of the terminal 

 bud. The cell of the first degree is wedge-shaped (PI. 

 XXXI, figs. 2 5), as is manifest by comparing its apical, 

 front, and side aspects. It is bounded by three curved 

 surfaces, the upper free wall of the cell representing a 

 portion of a spherical surface enclosed by two flattened 

 arcs, and the side-walls being two segments of a conical 

 surface. The septa which arise in the cell, and which are 

 alternately parallel to the one and the other of the simple 

 curved lateral surfaces, form cells of the second degree, 

 having the shape of the fifth part of an oblique hollow 



