4 LANG, Morphology of the Stock of Isoetes lacustris. 



Some preliminary remarks on the history of our 

 knowledge of Isoetes, and especially as to the various 

 interpretations of the morphology of the stock, will make 

 the reason for re-opening the question clear. It is only 

 necessary to deal with a few historically important papers 

 and with the main interpretations of the morphology. 

 Two such interpretations are apparent in the earlier 

 investigations that laid the foundations of our accurate 

 knowledge of the structure of Isoetes. The one was 

 clearly stated by Yon Mohl 4 in 1840; the other by 

 Hofmeister 5 in 1855. For our purpose it will be sufficient 

 to bring out the essential differences between the views of 

 these two investigators, and to follow the history of their 

 respective interpretations to the present time. 



In Von Mohl's clear and well-illustrated account of the 

 general macroscopic anatomy of the two-lobed stock of 

 Isoetes lacustris all the main facts of its morphology and 

 structure are shown ; the position of the cambium and of 

 the peculiar secondary zone is indicated in the figures, 

 although its nature was not recognised. Von Mohl de- 

 voted special attention to the arrangement of the roots on 

 the lower region of the stock. Recognising the shoot 

 nature of the upper portion of the latter, he discusses the 

 question whether Isoetes possesses a "caudex descendens" 

 on which roots are borne in acropetal order. He points 

 out that the roots can be regarded as standing in flattened 

 ellipses around a lower growing point drawn out in the 

 plane of the groove. The peculiar shape of the half-moon- 

 shaped, root-bearing region of the vascular axis is consis- 

 tent with this explanation. -The relationship of Isoetes to 

 other Vascular Cryptogams {Lepidodendron did not at 



4 t.iimaea, 1840. Reprinted in " Vermischte Schriiten,'* p. 122. 



B Abh. math.-phys. hi. d. K. Sachs. Ges. d. fViss., 2, p. 123. and later 

 in " Higher Cryptogamia" (1S62), to which references are made here. 



