20 GENERAL DIFFERENTIATION OF THE PLANT-BODY 



seen that this belief is erroneous, and that, bearing in mind the fact that 

 frequent change of function has taken place, we require x to read function 

 into the characters through which we diagnose organs. 



In the light of what I have said we may distinguish in the higher 

 plants 2 : 



(1) Vegetative organs, namely, root and shoot, with their appendages, 

 which may be grouped as hairs or emergences. 



(2) Propagative organs, namely, sporangia (including sporogonia), and 

 the sexual organs antheridia, and oogonia or archegonia. 



In the higher plants the shoot is differentiated into shoot-axis and 

 leaf in all cases except in some degenerate parasites. There are, it is true, 

 leafless shoots of limited growth, for example, the needle-like or leaf-like 

 assimilation-shoots in species of Asparagus, the bristles of the inflorescence 

 of Setaria and Cenchrus, but these are quite exceptions. It is remarkable 

 that in the most different cycles of affinity of plants in which the leaves 

 have been arrested a differentiation nevertheless takes place, which exhibits 

 clearly and without the necessity of careful morphological investigation 

 the construction characteristic of a leafy plant. The 'phylloclades' of 

 many monocotyledonous plants are the best known examples of this, 

 but we find similar features in species of Phyllanthus and in a number 

 of succulent plants both of the Cacteae and the Euphorbiaceae 3 . In the 

 lower forms of plant-life such a differentiation of the shoot may also 

 take place. The sexual generation of many liverworts and of the whole 

 of the mosses shows an evident division into shoot-axis and leaf, and, 

 as has been above explained, this condition is reached amongst the 

 liverworts in the most different cycles of affinity, which have developed 

 quite independently one of the other. That the leaves of the sexual 

 generation of mosses are not homologous with those of the asexual 

 generation of the Pteridophyta is sufficiently clear. Are we then to use 

 different names for them ? Such a proposal has already been made by 

 Bower 4 . But is there any advantage in this ? In my opinion it is 

 simpler to retain the old designation with the caution that it is based upon 

 analogy not upon homology. The more complex the technical terminology 

 is in a science, the more difficult it is to handle, and we must remember 

 that after all terminology is only a means to an end 5 . I have therefore 



1 How could a flower or a stamen be defined without reference to its function ? 



2 Pteridophyta and Spermaphyta. 



3 See my ' Pflanzenbiologische Schilderungen,' I., for figures. 



* Bower, On the limits of the use of the terms 'Phyllome' and'Caulome,' in Annals of Botany, i. p. 135. 



5 It is different when consideration of the homology induces us to put aside unnecessary terms. 

 The term ' corpuscle' for the archegonium of Gymnosperraae is now fallen quite out of use, and when 

 we use the term ' microsporangium ' for the pollen-sac, this is not the introduction of a new term but 

 only the transferring to the Spermaphyta of a term which is in common use when speaking of the 

 Pteridophyta. 



