STRUCTURE,] ORIGINAL CONDITION OF A LEAF. 273 



an ideal point, because the leaves or cotyledons are so close 

 together at their base, that they absorb, as it were, its whole 

 mass. Analogous circumstances are met with between the 

 integuments and nucleus of the seminal bud. 



The tumour of the axis is composed of a transparent 

 greenish mass, in which can be found some scattered granules, 

 a great quantity of cytoblasts, and lines of separation similar 

 to the sides of cells. This mass is coloured yellow by iodine. 

 When the tumour first appears, its surface is often furrowed, 

 which is due to the series of cells. The extreme edge of the 

 tumour is usually the most transparent, not only because its 

 mass is less considerable, but because the sap contained in 

 the last layer of cells is transparent. Under this layer the 

 mass is more opaque, and it is principally there that the 

 formation of the mother-cells takes place, at the expense of 

 which the axis grows from below upwards. 



Outside the centre of the top of the leafy axis, and always 

 nearer its apex than its base, there appears a small " excen- 

 tricity," which soon takes the form of a little rounded tumour, 

 and which, in consequence of the growth of the axis, is soon 

 clearly distinguishable from its summit. This first degree of 

 the growth of a leaf is absolutely identical in Exogens or 

 Endogens, and is the same for petals, stamens, and pistil. 



A lateral axis, at first very like this tumour, soon becomes 

 distinguishable from it. The lateral axis is not formed excen- 

 trically to the periphery of the top of the principal axis, but 

 on the same plane as the latter, so that the top of the principal 

 axis is divided by a slit into two equal portions. 



The birth of the leaf, in the form of an excentricity of the 

 axis, is distinctly seen in the embryo, where all confusion 

 with other organs is impossible. In Ecbalium agreste the 

 embryo globule is a cellular spherical corpuscle j at the point 

 furthest from the micropyle there is formed a slight depres- 

 sion, which grows gradually larger and larger, so that the 

 globule becomes furnished with two " excentricities," between 

 which the depression is found. At the point diametrically 

 opposite the hollow, and next the micropyle a little projection 

 is formed nearly at the same time, which grows larger and 



VOL. i. T 



