42 THE PALM-STEM. 



in thickness, which at the first glance seems to indicate a 

 great difference of its growth from that of the Dicotyle- 

 dons, is readily accounted for by the smaller size of the 

 lower part of its vascular bundles. That it does not in- 

 crease in thickness at all is not a perfectly correct state- 

 ment, for it certainly does exhibit a slight enlargement by 

 growth ; this increase of diameter occurs in many Palms, 

 for example, in Areca oleracea and Iriartea ventricosa, 

 not so much at the inferior extremity as higher up in the 

 stem, whence this acquires a spindle-like form. Since 

 the lower part of the bundles is not thicker than a hair, 

 it will be conceivable how many thousands of them may 

 be formed beneath the rind of the stem, without increas- 

 ing its diameter more than a single inch, which is so 

 slight a growth that it is wholly overlooked. 



I have already stated that the fibrous bundles in Dra- 

 caena become more strongly developed, and that the stem 

 then grows in thickness as in the Dicotyledons. From 

 the circumstance that these bundles, lying in the ex- 

 ternal layers of Dracaena, are nothing else but lower 

 extremities of the vascular bundles of the stem, it is most 

 evident that their growth and development is not to be 

 regarded as anything different from the growth of the 

 apex and the centre ; and that the idea of a double growth, 

 which Mirbel (Annal. du Museum, xiii, 67) imagined 

 that he found in Dracaena, Yucca, Aloe, Ruscus, Smilax, 

 Dioscorea, and Tamus, is no less incorrect than the idea 

 of the central vegetation generally attributed to the 

 Monocotyledons. 



Obs. 1. I have mentioned above that Moldenhawer had already expressed 

 himself against the correctness of the view of Desfontaines. Moldenhawer 

 distinguished in the same way, as has been done above, in every vascular 

 bundle of Zea Mays and Bambusa, in which plants his investigations were 

 chiefly made, liber, proper vessels, and wood; he also found that, in the 

 Grasses and Palms, the younger leaves were supplied by the outer, the older 

 by the inner vascular bundles, (Beitrage, p. 50.) 



Thus far, therefore, our researches fully accord ; but they differ in many 

 points in respect to the fibrous bundles devoid of vessels, and the origin of 

 the wood, the reason of which doubtless lies in the fact, that Moldenhawer 



