Anomalom Forms of Dicotyledonous Stems. 131 



without becoming blended with it. But here however, as in the 

 Malpighiacecey has been observed a disposition to separation of 

 certain portions of the wood from the central mass *. 



We require more investigation to enable us to determine the 

 relations of the structure of Phytocrene to that of the Bignoniacece', 

 especial attention should be paid to the conditions at different 

 periods of the growth. Jussieu opposes the opinion that the 

 plates passing inward from the bark belong to the liber, on ac- 

 count of the different structure of the liber observed in the same 

 stem. But since this difference consists in the fact, that, accord- 

 ing to Griffith t, they also contain striped vessels of small size, 

 while in the proper wood these are larger, in shorter joints and 

 of the dotted kind, the author does not think this is sufficient 

 reason to overset the idea that they originate from the liber. In 

 Nepenthes the ligneous twining stems, the bark, liber and pith, 

 are full of spiral-fibrous cells J, a proof that under certain cir- 

 cumstances these may occur in parts of the stem where they are 

 not usually found. 



Glancing retrospectively over the anomalous forms of dicoty- 

 ledonous stems we have enumerated, this much is evident, not- 

 withstanding the imperfection of the observations arising from 

 the want of materials : — the fibrous and vascular bundles de- 

 scending from the leaves are in general destined to be collected 

 around a common centre and there to become united together, 

 but yet in their ever-progressive vegetation a certain independ- 

 ence is retained by them, so that certain collections of them may 

 separate from the main body and be developed independently. 

 This development will at the same time proceed according to the 

 law of symmetry, i. e. they will arrange themselves around a 

 centre, and, in case the stem belongs to a dicotyledon, be placed 

 in a radiating series behind one another. What external cause 

 must arise, to produce such deviations from the usual mode of 

 gi'owth, cannot yet be determined for want of comparative obser- 

 vations, in the localities where these stems are found. Jussieu 

 conjectures § that one of the chief causes of these peculiarities is 

 the remote position of the leaves, the distance between them 

 being greater in the Lianes than in other plants. But the au- 

 thor says, that, if he is not mistaken, twining shrubs of the same 

 families are met with without the anomalous structure ; thus it 

 seems that some special impression must be received, which is 

 given to the formative principle by some external cause, such as 

 pressure in a particular direction, as mostly if not always happens 

 in climbing stems. It is well known that Bignonia radicans, also 



* Jussieu, Mem. Malpigh. 119. f Wallich, PI. Asiat. Rar. 216. 



X Korthals Verhandelingen, t. 20. § Cours de Botanique, t. 81. 



9* 



