131 
Anomalous Forms of Dicotyledonous Stems. 
without becoming blended with it. But here however, as in the 
Malpighiacea, 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 
jDlates 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. WTiat external cause 
must arise, to produce such deviations from the usual mode of 
growth, 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. 21G, 
t Korthals Verhandelingen, t, 20. § Cours de Botanique, t. 81, 
9 * 
