DISTINCTION BETWEEN MEMBERS AND ORGANS. 151 
generally appendages which may be termed hairs ; but there are never any roots 
in the morphological sense, and the term leaf, as understood in higher plants, can no 
longer be rightly applied even in those cases where the external form of the mature 
parts is similar to the foliage-leaves of higher plants, e.g. Laminaria digiiata, &c. 
It is now^ agreed to apply to those vegetable structures in which the morphological 
distinction of stem and leaves cannot be carried out in the present state of our 
knowledge (and which have never any true roots), the morphological term Thalhis 
or Thallome, In contradistinction to Thallophytes, all plants in which leaves 
can be morphologically distinguished might be termed Phyllophytes ; the name 
Cormophytes has, however, been given in preference to them. From what has 
been said it wdll be seen that the thallophyte is only distinguished from a cormophyte 
by the lateral outgrowths which occur somewhere or other on it not presenting 
sufficient morphological distinctions from the part which bears them, to permit us to 
term them leaves in the same sense as in the more highly differentiated plants. 
But as the morphological distinctions of stem and leaf are not yet sufficiently 
established even in higher plants, it is impossible to draw a sharp boundary 
between Thallophytes and Cormophytes, and indeed it is certain that one does not 
exist. 
If we now accept the terms Thallome, Stem (Caulome), Leaf (Phyllome), and 
Hair (Trichome)\ in the senses indicated, it can no longer be said that the leaf is the 
organ for this or that function ; for leaves may undertake all possible functions ; and 
the same remark applies also to the other parts. It is therefore on all accounts 
inexpedient simply to apply the term Organs to thallomes, stems, leaves, and hairs, 
for many of them have in fact no function at all. In order to avoid this mode of 
expression, which is confusing and foreign to morphology, it is obviously best to 
speak in this sense not of Organs, but of Members. The term Member is used w^hen 
we speak of a part of a structure in reference to its form or position, and not to any 
special purpose it may serve. Thus, from a morphological point of view, stems, 
leaves, hairs, roots, thallus-branches, are simply members of the plant-form ; but a 
particular leaf^ a particular portion of the stem, &c., may be an organ for this or that 
function, which it is the province of physiology to investigate. 
The morphological nature of a member is best recognised in its earliest 
stages of development, and by its relative position in the series of processes of 
growth ; the morphological definitions depend therefore essentially on the history 
of development. 
The older a member becomes, the more obvious becomes its adaptation to a 
definite function, the more completely is its morphological character often lost. In 
their earliest states the members to which the same morphological term is applied 
{e.g. all the leaves of a plant) are extremely similar to one another; at a subsequent 
period all those distinctions arise which correspond to their different functions. 
We can now arrive at a definition of Metamorphosis which may be used in a 
scientific manner : — Metamorphosis is the varied development of members of the 
same morphological value resulting from their adaptation to definite functions. 
^ See Nägeli und Schwendener, Das Mikroskop, vol. II. p. 591. 
