60 THE PALM -STEM : 



old stein, the condition was different, the greater number 

 of their vascular bundles being lost in the outer woody 

 layers of the stem, only solitary fibres curving upwards 

 or downwards, to run further beneath the rind. In the 

 roots of many other arborescent Monocotyledons he con- 

 stantly saw the vascular bundles, if the root were still 

 young, spread out like a star over the woody layer of the 

 stem; in older roots, on the contrary, they penetrated 

 deeper into the stem, where they then ramified and lost 

 themselves. Meneghini derives these differences from 

 the different conditions of the course of the sap ; the 

 main root (tap-root) and the lowest roots of the stem are 

 formed at the same time, and with the help of the same 

 currents of nutrient sap, as the vascular bundles of the 

 stem, the latter, therefore, pass directly into the fibres of 

 the former ; but when roots are formed on the older 

 parts of the stem, the currents of sap cause a stellate 

 expansion of their vascular bundles on the surface of the 

 woody mass of the stem. 



Unger has given some contributions to the knowledge 

 of the Monocotyledonous stem, having, in his researches 

 on the Dicotyledonous stem (Ueber den Ban und das 

 Wachsthum des Dicotyledonenstammes, 1840, p. 35), 

 taken a comparative glance at the structure of the Mono- 

 cotyledons, and, more particularly, subjected the stem of 

 the Aloinea (Draccena, Aletris, Yucca, Agave] to a more 

 minute investigation. With regard to the course and 

 anatomical peculiarities of the vascular bundles, Unger 

 agrees in general with the description I have given, and 

 thus nothing need be said on this point. But from his 

 investigation of the course of development of the vascular 

 bundles, he has been led to propound a definite opinion 

 as to the import of their proper vessels, while I had let 

 this point remain untouched. He traced the develop- 

 ment of the vascular bundles principally in the Aloinece, 

 and states that their rudiments are uniformly cellular, that 

 the other systems (the wood and liber portions) make 

 their appearance subsequently at the inner and outer 



