-100 SECRETION AND EXCRETION. 



66. Calcium oxalate. 



(a) Various forms of crystals in plant cells. 



(b) Comparison of the quantities of crystals present in young and old leaves. 



67. Water. 



(a) Exuded drops seen with the naked eye on various plants. 



(b) Part of a cleared leaf under the microscope showing a water-secreting gland 



with xylem vessels leading to it. 



68. Nectar secreted by the nectaries of a flower. 



