CHAPTER VIII. 



EQUISETACE.E. 



Equisetum arvense, pratense, variegatum, hjemale, palustre, 



limosum. 



The growing end of the stem of each shoot of the Equi- 

 setaceae consists of a blunt conical mass of cellular tissue, 

 and projects considerably beyond the place of origin of the 

 youngest leaf. The latter encloses the terminal bud in the 

 form of an annular cushion of uniform height. The next 

 youngest leaves are immediately underneath it, and closely 

 packed together. Their upper margins already exhibit the 

 first indications of the pointed lobes, into which the sheaths 

 which surround the base of each joint of the stem are pro- 

 longed (PI. XXXV, figs. 6, 7). 



The longitudinal growth of the stem* is produced by 

 repeated division of the large apical cell of the terminal bud, 

 which cell is three sided beneath, and sharply pyramidal. 

 The division takes place by means of septa which, following 

 a left-handed spiral direction, are successively parallel to 

 each one of the lateral surfaces (PL XXXV, figs. 3, 4). 

 The cells of the second degree thus formed divide imme- 

 diately twice over, by means of vertical septa which make 

 acute angles with the lateral surfaces of the cell and pass 

 to its free outer surface in a gentle curve concave towards 

 these lateral surfaces. That septum is usually formed first 

 which is seated upon the older side-wall of the cell 



* The cell -succession in the end of the stem of Equisetum was first correctly 

 described by Cramer (Nageli and Cramer, 'Pfianzen-physiol. Untersuch./ 

 Heft 4, Zurich). I had previously erroneously considered the form of the 

 apical cell to be that of a wedge. I have mentioned the cause of this erroneous 

 assumption in speaking of the cell-succession in the growing end of the stem in 

 Sphagnum. 



