10 THE STUDY OF PLANTS IN ANCIENT AND MODERN TIMES. 
sap, the idea being that identical primordial leaves issuing from the axis of a parti- 
cular plant were fashioned with more and more delicacy as the sap became clarified 
and refined in its passage through the vessels. This explanation of metamorphosis 
was first given by Goethe (1790) in a treatise which was much discussed, and which 
exercised a most important influence in initiating researches of a similar nature. 
Goethe’s interpretation of metamorphosis may be briefly reproduced as follows. A 
plant is built up gradually from a fundamental organ—the leaf—which issues from 
the node of astem. First of all, the organs which are called seed-leaves or cotyledons 
(fig. 1) develop on the young plant as it germinates from the seed; they proceed 
from the lowest node of the stem, and are frequently subterranean. They are of 
comparatively small size, are simple and unsegmented, have no trace of indentation, 
and appear for the most part as thick, whitish lobes, which are, according to Goethe’s 
expression, closely and uniformly packed with a raw material, and are only coarsely 
organized. Goethe explains these leaves as being of the lowest grade in the evolu- 
tionary scale. After them and above them the foliage leaves develop at the suc- 
ceeding nodes of the stem; they are more expanded both in length and breadth; 
their margins are often notched, and their surfaces divided into lobes, or even com- 
posed of secondary leaflets; and they are coloured green. “They have attained to 
a higher degree of development and refinement, for which they are indebted to the 
light and air.” Still further up, there next appears the third stage in foliar evolu- 
tion. The structure called by Linnzeus the calyx is again to be traced back to the 
leaf. It is a collection of individual organs of the same fundamental type, but 
modified in a characteristic manner. The close-set leaves, which proceed from 
nodes of the stem at what is, in a certain sense, the third story of the plant-edifice 
as a whole, and which constitute the calyx, are contracted, and have but little variety 
as compared with the outspread foliage-leaves. 
On the fourth rung of the ladder by which the leaf ascends in its effort to perfect 
itself, appears the structure named in the Linnzan terminology the corolla. It 
consists, like the calyx, only of several leaves grouped round a centre. If a con- 
traction has taken place in the case of the calyx, we have now once more an expan- 
sion. The leaves which compose the corolla are usually larger than those of the 
calyx. They are, besides, more delicate and tender, and are brightly coloured; and 
Goethe, whose mode of expression is here preserved as far as possible, supposes them 
to be filled also with purer and more subtle juices. He conceives that these juices 
are in some manner filtered in the lower leaves and in the vessels of the lower 
region of the stem, and so reach the upper stories in a more perfect condition. A 
more refined sap must then, he says, give rise to a softer and more delicate tissue 
(fig. 2). Above the corolla and at the fifth stage of development there follows the 
group of stamens, structures which, though not answering to the ordinary conception 
of leaves, are yet to be regarded again simply as such. In the circle of the corolla 
the leaves were expanded, and conspicuous owing to their colour; on the other 
hand, in the stamens they are contracted to an extreme degree, being almost fila- 
mentous in part. These leaves appear to have reached a high degree of perfection, 
