2 Lang, Morphology of the Stock of Isoetes lacustris. 



with the shoot as the rhizophore or rhizophoric region of 

 the stock. 



To determine the place of a plant in the natural 

 system and its relations to other plants, living or extinct, 

 is one of the objects with which morphology is studied. 

 The morphological problems presented by a plant are, 

 however, by no means solved when its affinity or phylo- 

 geny is determined with reasonable probability. This 

 holds for Isoetes, where indeed the probable phylogeny 

 adds greatly to the interest of the study of the morphology. 



Various affinities have at different times been sug- 

 gested for Isoetes, but there appears to be preponderating 

 evidence for the view that it belongs to the Lycopodiales 

 and is most directly related to the heterosporous arbores- 

 cent forms that flourished in the Palaeozoic period. This 

 view has been stated in more recent times by, among 

 others, Potonie, 1 Scott 2 and Bower, 3 all of whom have 

 studied Isoetes in the light of comparison with the extinct 

 plants forming the Lepidodendreae in the wide sense, or 

 as they are sometimes called, the Lepidophytinae. This 

 affinity is expressed in Potonie's treatment of the groups 

 concerned in the " Naturlichen Pflanzenfamilien," and 

 most recently by Scott in his book on " The Evolution of 

 Plants." After considering the features of the Lepido- 

 dendreae and of the Triassic plant Plcuromeia, Dr. Scott 

 sums up the question by saying that the Lepidodendreae 

 " may have become wholly extinct early in Mesozoic 

 times, or may possibly have left a dwindling race of 

 degenerate descendants, which reached their final stage of 

 reduction in the dwarfed plantlets of the amphibious 

 Isoetes." With this view of the probable relationship of 



1 "Nat. PflanzeDfamilien." 



2 "Evolution of Plants." 



3 "Land Flora." 



