and Growth of Monocotyledons. 181 
far as I can at present judge, the various forms are all redueible 
to two types, which are themselves united under the single com- 
mon character which was first definitely announced by Schleiden. 
Those who are acquainted with his views will recollect that he 
has pointed out an essential distinction between the charaeters 
of the fibro-vascular bundles of Monocotyledons and of Dicoty- 
ledons, which in the former are closed-, that is, their growth in 
the transverse direction is arrested at a definite epoch, whence 
results their isolated condition, giving a peculiar aspect to the 
monocotyledonous stem; while in the Dicotyledons the fibro- 
vascular bundles not only grow laterally, so as to come in con- 
tact with one another as wedge-shaped bodies collectively form- 
ing a ring, but their peripherical or external face is capable of 
development to an extent only limited by the life of the plant 
in which they exist. Thus the successive layers which add to 
the thickness of a dicotyledonous stem are produced by the pe- 
ripherical growth of the fibro-vascular bundles, the distinction 
into rings, frequently so strongly marked, depending merely on 
the difference of the condition of those elements of the fibro- 
vascular bundle produced in the earlier part of the year from 
that of those formed during the advance of the season. 
This is the sole universal character by which the stems of the 
two great classes can be distinguished. The theoretical distinc- 
tion into Endogens and Exogens has not a single fact to support 
it. All plants possessing a stem are Endogens so far as the 
origination of organs is concerned, since these are developed in 
buds in the axils of older organs, and, in terminal buds, are im- 
mediate developments of the central parenchyma. But the new 
deposits of fibro-vascular structure belonging to these are found 
crossing those of the older organs at the earliest period of their 
development, and always and in all stems come to be applied 
upon their outer surface. The accounts of endogenous growth 
are negatived by all those who have traced the development of 
Structure in the Monocotyledons, and could only have been 
founded on a superficial examination of fully-formed stems. I 
have traced the development in the buds of many of oui’ indi- 
genous and commonly cultivated Monocotyledons, and they all 
agree with the characters of that one which I have selected to 
illustrate this point. 
In the accompanying drawings (PI. IX. figs. 2 and 3) are re- 
presented sections of very young buds of Spai-ganium ramosum, 
and the nascent fibro-vascular bundles are seen in the central 
portion ; the uppermost and youngest, much more delicate and 
less perfect than the lower, being in direct connexion with the 
central nascent leaves. The figures also illustrate several other 
important points concerning the structure of monocotyledonous 
