THE HIGHER CRYPTOGAMIA. 239 



each two divisions always increases to nearly the original 

 size, become especially active in the direction of the mar- 

 ginal angle formed by these two side- walls. This w T ill 

 cause its form to vary more and more in the manner above 

 pointed out, until the relation between the angles required 

 by the hypothesis is attained. It is easy to imagine that 

 any excess of aperture is prevented by the proportion of 

 the rapidity of the progress of the multiplication of the older 

 secondary cells to that of the youngest. 



In the course of the long inquiries leading to these results, 

 I met with only one isolated fact which militated against 

 the conclusions arrived at. I found the apical cell of a 

 terminal bud of Aspidium spinulosum, the base of whose 

 upper surface measured 41/248 m.m.m., and each side 

 97*808 m.m.m. The stem, which had the left-handed 

 T | arrangement of the fronds, was growing at the edge of 

 a ditch, amongst a mass of briars, being half buried in the 

 earth, and directed downwards : the joints of the stem 

 were unusually elongated. It is probable that the plant was 

 in an abnormal, perhaps in a diseased condition. 



The two-edged form of the apical cell, and the bilinear 

 arrangement of the fronds, of Pleris aquilina, have been 

 already observed upon. The same coincidence is always 

 met with (as far as present observations extend) in 

 Niphobolus rupestris and N. Lingua, in Polypodium punctu- 

 latum, P. cymaiodes, and P. aureum, and very frequently 

 in P. vulgare and Dryopteris. 



The determination of the cell-succession in the apical 

 region of the leaf-buds of phsenogamous plants is attended 

 with considerable difficulties. The minuteness of the ele- 

 mentary organs is the least obstacle ; a more formidable 

 one, especially in the Coniferse and Dicotyledons, is the 

 very early occurrence of rapid and vigorous multiplication 

 of the secondary cells of the flat end of the bud. It is not 

 always that the terminal cell of the bud can be ascertained 

 with certainty. Where however this was done the form of 

 this cell corresponded with the phyllotaxis ; it was two- 

 edged in the grasses (Sccale cereale, Phray mites arundinacea) 

 and in species of Iris ; and often of the same shape in trees 

 with decussate leaves {Acer, Fraxinus, Cupressus). Here 



