MR. T. Н. CORRY ON ASCLEPIAS CORNUTI. 177 
were first excreted become carried successively more and more to the exterior of the mass. 
As the gum dries it becomes darker, and changes from colourless to a light golden-yellow, 
then to dull brownish yellow, and finally to dark black or reddish brown. It is never at 
any period green, as it is stated to be at first by Schleiden *. It likewise becomes very hard, ` 
and assumes almost the consistence of horn or cartilage; but its original structure is still 
to be seen in transverse section, especially in the part in contact with the excreting 
cells, which is still viscid and semifluid. The excretion of this gum appears to take place 
first from the cells forming the sides of the furrow, and only at a later period from those 
forming the floor; and as the liquid gum is exuded it flows down towards the base of the 
furrow, so that, soon after the membrane stage, two slender, parallel, partially hardened, 
masses of gum, more or less resembling quadrants, and of a light-brown colour, are found 
lying in the groove. They are still, however, quite distinct from each other, being sepa- 
rated by the cells forming the median floor of the groove, which have not yet begun to 
excrete (fig. 14). Ав the growth of Ше style-table proceeds, the two masses of partially 
hardened yellow gum which lay at the base of the furrow side by side with the angles of 
the quadrants, directed laterally in the previous stage, have been carried upwards, and are 
now to be found adhering laterally to the cells, which at this period form the mouth of 
the furrow, but which were originally situated near its floor (fig. 15). Іп this process the 
angle of each quadrant has been rotated through an angle of 45°, so that now the masses 
of gum project and partially roof over the open mouth of the groove. Excretion then 
takes place from all the cells forming the sides of the furrow, and so, by successive addi- 
tions from behind, the quadrant-shaped masses are more closely approximated, while at 
the same time the sides of the future corpusculum are formed. The cells forming the floor 
now begin to excrete, so that the two masses of hardened gum become joined together 
posteriorly by less hard material, which is therefore of a lighter colour. This junction 
takes place first at their upper extremities where the groove is narrowest across, and 
gradually proceeds backwards, the two hardened masses being in consequence first united 
above posteriorly and lying close together but still ununited for the rest of their length, 
and then afterwards united posteriorly along their whole length, but so delicately at this 
time that the mass tears into two parts posteriorly when its removal from the furrow is 
attempted. 
The cells forming the extreme borders of the furrow likewise excrete, and their liquid 
excretion, flowing down and hardening, augments the thickness of the corpusculum above 
on its antero-lateral angles. 
This hardened mass of gum, the apparently cellular structure of which is caused by 
the impression of the underlying cells which excreted it, and to which it was at first 
adherent (for it is really formed of pseudomorphs of cells +), has been dignified by Jussieu, 
Robert Brown, Payer, and others as a “gland,” and by others again as a “ stigmatic 
* Grundzüge, English translation, p. 382. 
t 2. the retinacula of the Orchids, which, according to the researches of the younger Reichenbach, “Пе 
Pollinis Orchidacearum Genesi ac Structura,’ Leipsic, 1852, are formed of true cells, which are metamorphosed and 
secrete a fluid, and are therefore of a glandular nature, though they serve a somewhat analogous function to these 
masses of gum in Asclepias. 
