10 THE STUDY OF PLANTS IN AXCTEXT AXD MODERN' TIMES. 



sap, the idea beinf^ that identical primordial leaves issuing from the axis of a parti- 

 cular plant were fashioned with more and more delicacy as the sap became ciaritied 

 and refined in its passage through the vessels. Tliis 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 a stein. First of all, tlie organs which are called seed-leaves or cotyleilons 

 (fig. 1) develop on the young plant as it germinates from the seed; thej- proceed 

 from the lowest node of the stem, and are frequently subterranean. Thej' 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 coai"sely 

 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 Linnaeus the calj^x is again to be traced liack 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 storj' 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 a.scends in its efibrt to perfect 

 itself, appears the structure named in the Linnsean terminologj^ the corolla. It 

 consists, like the calj^x, only of several leaves grouped round a centre. If a con- 

 ti-action 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 ordinarj- 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 coloiu"; 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 i-eached a high degree of perfection, 



