PHYSIOLOGICAL BOTANY. 235 



increase in length towards the upper part, and finally be- 

 came very long. But the cells at the circumference of the 

 root were longer than those in the centre. In all of them 

 the inner membrane was separated from the walls of the 

 cells, and was contracted around the granular contents, 

 which were of a dark brown colour. The sac thus formed 

 assumed the shape of the surrounding cells, the walls of 

 which did not appear at all coloured by the iodine. Each 

 cell contained the globular sac, which I denominated the 

 secondary cell above ; it was also of a brown colour, and 

 filled with a granular mass. It was always situated in 

 the longer sac, but in different cells sometimes at the 

 ends, sometimes in the centre, sometimes near the centre. 

 Thus, where the growth was most active, short cells ap- 

 peared to have been formed, which then became elongated 

 and had completed their growth. I could not satisfac- 

 torily perceive any division of cells. I had made similar 

 marks to those upon the roots, on the young leaves which 

 sprouted out from the same bulb ; one near the bulb, 

 another just beneath the apex, and a third midway 

 between the two other marks. That nearest the apex 

 remained unchanged ; the apex of the leaf, just as the 

 apex of the root, did not grow ; that portion between the 

 mark on the apex and the middle had increased but little, 

 just the reverse of what occurred in the roots, in which 

 this was the part which had grown most, whilst that part 

 of the leaf near the base had increased very considerably, 

 whilst in the roots, on the contrary, it had grown but little. 

 A longitudinal section of a marked leaf was then made 

 parallel with its surface, from the base of the leaf at the 

 root upwards, and treated as before. In this case, as had 

 previously been found in that of the root, short but not 

 broader cells were found at the base of the leaf near the 

 root, where the growth commenced, and these increased 

 in length upwards, towards the middle of the leaf. The 

 formation of these short cells and their elongation evidently 

 produces the increase in size of the leaf, as I have already 

 remarked in my < Lectures on Botany/ (p. 83,) and have 



