Manchester Memoirs, Vol. lix. (191 5), No. %. 5 



this date enter into the comparison) is a difficulty in recog- 

 nising a " caudex descendens." In other Vascular Crypto- 

 gams such a region is wanting, the adventitious roots being 

 borne in ascending order on the shoot. If, however, the 

 roots of Isoetes are regarded as adventitious they present 

 a remarkable exception to the order in which roots arise 

 in other plants. Von Mohl left the important question, 

 he had so clearly raised, in some degree open, while evi- 

 dently inclining to the view that the roots in Isoetes do 

 arise in acropetal succession in relation to a peculiarly 

 shaped, downwardly growing region of the stock. 



Another interpretation of the stock oi Isoetes was given 

 in the classical work of Hofmeister and has remained on 

 the whole the accepted view to the present time. The 

 acropetal succession of the successive series of roots in 

 relation to a downwardly growing region is admitted but 

 explained as " only an apparent irregularity, depending 

 upon the unusually vigorous development of the bark, and 

 its yearly renovation from within outwards." The roots 

 are regarded as standing in vertical lines parallel to the 

 the grooves and in each vertical line the oldest roots are 

 said to stand nearest to the base of the stock and the 

 youngest nearest to the stem apex. For further details of 

 Hofmeister's interpretation of the arrangement of the 

 roots of Isoetes, reference must be made to the original 

 account, which on this subject is not altogether clear. 

 What has been said will show how it differs from Von 

 Mohl's interpretation, although on both the root-bearing 

 region of the stock of Isoetes is seen to be peculiar and 

 anomalous among existing Vascular Cryptogams. 



Von Mohl's interpretation, which recognised the root- 

 bearing region as in a sense the correlative of the shoot, 

 was practically replaced by Hofmeister's, and hardly 

 figures in the literature until recently. In 1909 Miss 



