Manchester Memoirs, Vol. lix. (191 5), No. 8. 33 



Besides the usual, marked, anomalous secondary 

 thickening, Scott and Hill call attention to other mani- 

 festations of secondary growth. In two cases a cambial 

 layer was observed arising internal to the first, and 

 presumably later than this, from the parenchymatous cells 

 immediately outside the xylem ; this cambium, like the 

 usual anomalous one, produced all three tissues (phloem, 

 wood and parenchyma) on its inner face. Still more 

 interesting, however, is the reference to indications of 

 secondary growth in a normal position, the cambium 

 lying between the primary xylem and the phloem ai.d 

 adding a few elements of secondary xylem in immediate 

 contact with the primary wood. The distinction between 

 the activity of this normal cambium and the anomalous 

 cambium is not, however, quite clearly made. Attention 

 has been drawn to these particular points in Scott and 

 Hill's description, because they will be seen to be in 

 agreement with some distinctions that will be made below 

 in the stelar structure of Isoetes lacustris. 



Previous work and opinion on two intimately related 

 questions, the apical growth and the cauline or common 

 nature of the stele, must also be briefly referred to. 

 Hofmeister referred the apical growth of the stem to a 

 single initial cell. Later investigators (Bruchmann, 7 Hegel- 

 maier, 8 Farmer, 9 Wilson-Smith 10 ) have regarded it as due 

 to an apical group of cells. Scott and Hill, 11 on the whole, 

 agree with this latter view, while pointing out that the 

 appearances in some cases suggest the presence of a 

 single apical cell. The decision of this question is of less 



u lot. cit. 



"'Jena. Zeitschrift (1874). 



8 Rot. Zeitung (187 4). 



!) Annals of Rot any, V '. (1890). 



I ° Botanical Gazette, XXIX. 



II toe. tit. 



