33 
botanists who included these plants sometimes with algae and 
sometimes with fungi. Ndageli* placed them with the algae under 
the family Lichenaceae, stating that they agree in vegetative 
habit with the Stilophoreae and Fucaceae. So-called modern botany 
persists in placing lichens with fungi, a procedure which the au- 
thor has always considered unnatural and unscientific, because 
morphologically lichens resemble green assimilating plants (algae, 
etc.) and not fungi. Morphological conformation and habit is in 
all cases the expression of the organization of plants as they de- 
velop in obedience to the requirements of biological existence. 
Sometimes plants that are widely separate as to their habits 
show a great similarity of form. Nothing would however be 
farther from the truth than to assume that these similarities of 
gross appearance were due to identical or similar causes. As an 
illustration is cited Clavaria flava and Cladonia uncials. In both 
the anatomical conformations secure a maximum of surface-expan- 
sion. In the former plant this is for the special purpose of further- 
ing reproduction, in the latter for the special purpose.of furthering 
assimilation. A few similar illustrations are given, which em- 
Phasize the necessity of giving correct physiological interpreta- 
tions to the structural conformations. 
The author now enters upon a highly theoretical discussion of 
classification. A system may be either practical and artificial or 
theoretical and natural. Furthermore, the modern natural system 
is supposed to be built upon the basis of phylogenesis. The author 
has purposely refrained from designating the natural system as 
Scientific, since the artificial system is likewise scientific. _ 
There is no sound basis upon which to build a phylogenetic 
system. Paleontology fails us in the consideration of the most 
important questions; this is particularly true in the phylogeny of 
the thallophytes. Here we are almost entirely dependent, upon 
evidence deduced from a study of the comparative morphology of 
' existing plants. But what scientific right have we to formulate 
conclusions from such comparisons? What evidence have we of 
the genetic relationship of plant-types? The emphatic causes 
that ontogeny represents phylogenetic development is nothing 
Nagel, K. Die neuen ‘Algensysteme, und Versuch zur Begriindung eines 
. 4 
Signen Systems der Algen-und Florideen, Zitrich, 1847 
