200L0GY AND BOTANY, MICROSCOPY, ETC. 
815 
Stem of Wistaria.* — Mr. C. C. Curtiss describes a peculiarity ob- 
servable in old stems of Wistaria sinensis. After growth has continued 
normally for a series of years, usually twelve or more, a new cambium 
zone is formed outside the primary bast, and the old cambium dies. The 
growth of this secondary cambium continues for perhaps eight years, 
and then it dies and the same process is repeated. This method of 
development continues through life, stems twenty-five years old showing 
four or more bast-zones. All the elements of the wood, the xylem, 
phloem, and periblem, receive their proportional annual increase with 
wonderful regularity, and the bast is of extraordinary strength. The 
structure of the various elements of the stem is described with great 
minuteness. 
(4) Structure of Organs. 
Metamorphosis and Idiomorphosis.f — Prof. F. Delpino regards the 
leaf, not as an independent organ, bat as a section of a merithallus, 
the free projecting portion of a cone of growth, the remaining elements 
of which are closely united with one another to form the axial shoot. 
Of the various transformations of the leaf, the foliage-leaves, coty- 
ledons, anther-lobes, and carpels are prototypic and primordial, as 
contrasted with the sepals, petals, tendrils, pitchers, &c. Of the coty- 
ledons and foliage-leaves, the latter is probably the primeval form. The 
metamorphosis may be of many different degrees ; of a low degree are 
scales, spines, tendrils, &c. ; of a higher degree such organs as the 
perianth of Aquilegia. The homologous organs of different plants are 
not always of the same degree of metamorphosis ; thus, the calyx of 
Malvaceae is an involucre, that of Helleborus a true calyx, that of Kosacese 
a modification of the foliage-leaf, that of Tradescantia a modification of 
the corolla, &c. 
The author applies the term idiomorphosis to certain special kinds of 
metamorphosis ; such as that by which the petals of Camellia result 
from a modification of the bundles of stamens, as is shown in partially 
double flowers. Of the same nature are the petaloid sepals of Polygala , 
the petaloid bracts of Salvia , the petaloid involucre of Astrantia , the 
petaloid androeceum of Atragene and Nymjphsea , &c. 
Vegetable Statics. t — From experiments made on different plants 
M. A. Letellier is led to assert that segments of a root or stem, while 
still in a meristematic condition, float in a liquid of suitable density in a 
direction which is the same as that manifested during life. Hence he 
concludes that the orientation of the young parts of a plant is that which 
corresponds to a position of stable equilibrium. Descending roots have 
their centre of gravity below their centre of measurement ; while in 
stems and ascending roots the relative position of the two centres is 
the reverse ; rhizomes and secondary roots have their two centres so 
near to one another that their equilibrium is nearly indifferent. From 
mathematical reasoning, the author derives the two following laws: — 
(1) The plant grows in the direction which favours its position of stable 
* Journ. New York Micr. Soc., viii. (1892) pp. 79-89 (3 pis.). 
t Mem. R. Accad. 1st. Sci. Bologna, ii. (1892) pp. 101—17. See Bot. Centralbl., 
li. (1892) p. 274. 
X Comptes Rendus, cxv. (1892) pp. 69-72. 
