of the terms 'Phyllome ’ and 'Caulome! 145 
Again, it may be urged that if this distinction, based on a 
want of homology, be marked by a difference of terms, the 
student will conclude that all those developments which are 
termed ‘ phyllome ’or * caulome’ are lineally connected, and 
likewise all those called ‘ phyllidium’ and ‘ caulidium’ : this 
difficulty would, however, be due to a process of defective 
reasoning from which the student must take care to guard 
himself. The fact is that it is not clearly desirable that every 
recognised case of want of homology of homoplastic members 
should be distinguished by definite terms, nor is our know- 
ledge sufficient as yet to justify an extensive use of phylogeny 
in checking the nomenclature of morphology, even if it were 
desirable. 
Again, it may be argued that observations of apogamy and 
apospory show that the two alternating generations are not so 
distinct from one another as has been supposed. This ob- 
jection is virtually answered in another place 1 , where the 
opinion is expressed that such observations as those of apo- 
spory do not indicate a reversion bearing a deep morphological 
meaning, but are rather to be regarded as mere sports. 
In thus proposing to recognise more fully the fact of parallel 
development in the terminology of the science no new principle 
is made use of : it is merely intended to bring generally ac- 
cepted conclusions into greater prominence, so as to obtain a 
clearer view. It is, however, a move exactly in the opposite 
direction to that recently made by Prof. Sachs. In his Lectures 
on the Physiology of Plants he brings together under a com- 
mon name homoplastic organs of radically different origins 2 . 
Though this system of physiological organography is an un- 
doubted advantage to the physiologist, who, in pursuing his 
special line of study, will necessarily centre his attention on 
the individual rather than on the race, the use of the old terms 
in a new sense, which disregards such conclusions as are based 
Fissidens to the phyllome of Iris or Narthecium ; but it is exactly in these cases 
that it is most necessary to keep clearly before the mind the fact that these 
members are not lineally related, but are only analogous to one another. 
1 Trans. Linn. Soc. vol. ii. p. 322. 2 Annals of Botany, vol. i. p. 84. 
