and Growth of Monocotyledons. 181 



far as I can at present judge, the various forms are all reducible 

 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 characters 

 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 pi-oduced 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 our indi- 

 genous and commonly cultivated Monocotyledons, and they all 

 agree with the characters of that one which I have selected to 

 illustrate this point. 



j^In the accompanying drawings (P!. IX. figs. 2 and 3) are re- 

 presented sections of very young buds of Sparganium 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 



