228 HOFMEISTER, ON 



base where it suddenly ceases, and which is accompanied 

 by a series of divisions proportionate in number to the in- 

 crease of the circumference of the cone and produced by 

 longitudinal septa radial to the axis of the stem) — whilst the 

 division by transverse septa at right angles to those chorda! 

 longitudinal septa occurs proportionably seldom. The 

 conical terminal bud grows upwards by the formation be- 

 neath its entire outer surface of a layer of cells having the 

 form of a conical covering thicker towards the base, whilst 

 the angle of inclination of the cone becomes continually 

 narrower. At a latter period, after the formation of the 

 rudiments of several cycles of fronds, the longitudinal 

 growth of the stem is so much accelerated by the active ex- 

 tension of the cells of the axile tissue (accompanied by the 

 formation of transverse septa in the peripheral cells) that it 

 exceeds the previous increase in thickness. The cortical 

 region is pushed outwards by the longitudinal extension of 

 the middle of the stem, and. passes from the form of a very 

 blunt cone into that of a cylinder ; this complete inversion 

 of the mode of growth is caused by the change of direction 

 of the expansion and multiplication of the cells. The 

 process (which is common to all stems with flat terminal 

 buds, e. g., Polytrichum, Dracaena) is more easily seen in the 

 slender stem-ends of the germ-plants and gemmae of 

 Aspidium filisc-mas or Aspleniwn filix-femina, than in the 

 stems of older individuals of the former plant which become 

 too thick. 



After the stem of the germ-plant has increased in thick- 

 ness the arrangement of the subsequent new fronds changes 

 from the \ to the § arrangement. At the same time the 

 distribution of the vascular bundles in the stem becomes 

 different. At the place where the vascular bundle which 

 passes into the last frond of the \ arrangement turns side- 

 ways, strings of the cambium which afterwards forms the 

 vascular bundles separate themselves in the direction of 

 each of the three next fronds, and run parallel to the longi- 

 tudinal axis of the stem (PI. XXVI, fig. 15). A trans- 

 verse section of the stem at this spot exhibits three vascular 

 bundles arranged in a circle (PL XXVI, fig. 16). 



The rudiments of the vascular bundles which pass to all 



