STRUCTURE.] PALM-STRUCTURE. 227 



of woody tissue in Exogens, in which there is no such 

 arrangement of woody tissue, so called vasa propria, or spiral 

 vessels. 



Very accurate and elaborate inquiries into the structure 

 and development of Endogens have been instituted by Mirbel, 

 who does not admit that the woody bundles proceed from the 

 leaves ; but believes that he has proved their origin to be 

 independent, in the growing point, or phyllophore, as he terms 

 it, whence they lengthen upwards, introducing themselves 

 into the leaf, and downwards, passing through the medul- 

 lary matter of the stem. Von Martius gives the following as 

 his latest opinion of the true structure of Palms, after a 

 consideration of all the evidence that had been collected 

 in April, 1845 : 



1. The stem of Palms does not contain more woody 

 bundles than are destined to enter sooner or later into the 

 leaves. 



2. The woody bundles originate on the summit of the 

 stem, in the growing point or phyllophore of Mirbel, between 

 the new and plastic parenchyma which there forms a peculiar 

 conical layer, covering, like a funnel, the more aged parts. 

 They are always external with relation to those which are 

 already formed, and a little higher. 



3. The points of origin of the woody bundles are organi- 

 cally predetermined; we find, in these points, the fibres 

 situated obliquely, and converging at their upper ends. 

 They lengthen from both ends that is to say, they grow 

 from below upwards, and from above downwards. 



4. The upper extremity of these woody bundles is directed 

 towards the base of the young leaf; the latter originates in 

 the form of a cellular fold in the centre of the bud, and is 

 directed towards the circumference on becoming enlarged. 



5. The lower extremity is extended obliquely downwards, 

 and terminates, in the form of an extremely slender and 

 mere parenchymatous filament, upon a layer at the circum- 

 ference. This layer is wholly different from the liber of 

 Dicotyledons in development ; it may, however, be compared 

 to that part of their system as regards its constituent 

 elements. 



Q2 



