WATER- STOM ATA 141 



tissue, and constitute a firm framework, the interstices of which 

 are filled with the thin- walled parenchyma. 



Compare also the tissue of the mesophyll in the lamina of 

 Camellia and Hoy a, throughout which sclerenchymatous elements 

 are irregularly distributed. 



III. Water-stomata and marginal glands. Examine leaves 

 of the Fuchsia, and observe that the tips of the leaves and the 

 marginal teeth are terminated by slightly swollen, opaque masses 

 of tissue : these are the marginal glands, and drops of water 

 exuded at those points may be seen in the morning, or on plants 

 kept during the day in moist atmosphere at a high temperature. 



Cut off a piece of the margin of a leaf and examine it under a 

 low power : a large stoma (water-stoma) may be recognized at the 

 apex of each tooth : below it is a pad of opaque tissue (the gland) 

 to which a vascular bundle runs up, and in which it ends. 



From material which has been hardened in alcohol, cut off with 

 a razor the extreme tips of several of these teeth : mount with the 

 outer surface uppermost : on examining these, the extreme apex, 

 with the water-stoma, will be seen in surface view. Note the 

 size of the stoma, and that the pore is widely expanded : a camera 

 lucida drawing of the water-stoma should be made, and compared 

 with a similar drawing of an ordinary stoma from the same leaf : 

 it will then be seen that the water-stoma is of larger size. 



Cut longitudinal sections so as to follow the vascular bundle up 

 to the marginal gland, and to traverse the gland in a median 

 plane. Selecting a section which is really median, note, in the 

 part of it further from the tip, the epidermis, mesophyll, and the 

 vascular bundle surrounded by a parenchymatous sheath : follow- 

 ing these up towards the tip, observe th eepidermis continuous, 

 with the exception of the widely-gaping water-stoma at the ex- 

 treme apex : the form of the guard-cells as seen in section is 

 simpler than in ordinary stomata. The vascular bundle widens 

 out towards the tip, and the vascular elements terminate in the 

 pad of closely packed parenchyma of the gland (epithema) 

 there is a large cavity below the water-stoma. 



Similar observations should be made at the points of exudation 

 of water in leaves of Primula sinensis, Tropceolum, &c. 



Special attention should be paid to the chalk-glands of the 



