Problems of Plant Physiology 41 



to the laticiferous system; the significance of the Casparian strips; 

 and the meaning of guard cell fusion in Azolla and Funaria (11). 

 Haberlandt was able to grow sporangia of Funaria in a culture solution 

 for three weeks during which time normal spores were formed thus 

 showing the efficiency of the chlorophyll system (11). The so-called 

 secretion of wax by certain stomata requires further study (11). Un- 

 certainty exists with reference to the secretions of certain glands as 

 capitate and scutate ones (11) and elaioplasts (18). Objections have 

 been offered to Tyndall's (11) interesting investigations concerning a 

 layer of air saturated with ethereal oil which it is argued protects 

 the parts concerned against heat, cold, or excessive transpiration. Do 

 enzyme reservoirs contain protein material in addition to the enzyme 

 (11) ? Why are such large amounts of lime required for plants with 

 cystolithic structures (11) ? 



There is the difficult problem of the dehiscence and cohesion mech- 

 anism of anthers, sporangia and other structures (11) which has 

 occupied the attention of so many observers and has been so often the 

 topic of research. Although these cases are of a physical nature, they 

 are also of physiological interest and are still partly unsolved. The 

 immense amount of work done on living motor tissues in the Urticaceae, 

 Stylidium adnatuvi, and Cyclanthera explodens leave many points in 

 doubt (11). It is moreover, remarkable that tactile pits have thus far 

 been found in the walls of sensory cells only in the Curcurbitaceae and 

 possibly also the Sapindaceae and tactile papillae only in floral organs 

 and tendrils (11). The work on tactile organs of carnivorous plants, 

 first recognized by Edwards in 1804, (11) leaves much to be done. In 

 Drosera rotundifolia, Darwin found that a hair weighing .000822 milli- 

 gram produced a noticeable reaction (1, Bd. II, p. 461) while, according 

 to Kemmler, the least weight that will produce a stimulus on a sensitive 

 skin is .002 milligram (1, Bd. II, p. 423). The causes of certain changes 

 in the rate of growth of tendrils are unknown (1, Bd. II, p. 443). The 

 epidermal lens cells of the epidermis as studied by Haberlandt present 

 an interesting field worthy of further study. His photographs of a 

 portion of a microscope made in connection with one of the membrane 

 lenses show their capabilities (19). 



The transmission of stimuli varies according to the kind of stim- 

 ulus. Thus, Czapek (20) and others state that geotropic and heliotropic 

 stimuli travel two millimeters in five minutes. Traumatic stimuli, ac- 

 cording to Kretschmar (21) travel one to two centimeters per minute 

 and Fitting (22) gives the rate as one to two centimeters per second 

 for the tendrils of Passiflora coerulea. In Minniosa piidica the velocity 

 is about 1.5 centimeter per second (11). Questions as to the exact part 

 played by the protoplasmic threads between the protoplasts are unan- 

 swered. Chemical stimuli in Drosera are transmitted only about ten 

 millimeters per minute. Darwin found that .000423 milligram of am- 

 monium phosphate would cause curvature of a tentacle (1, Bd. II, p. 

 463). The question remains as to what response if any is due to ex- 

 ternal causes. The origin of certain stimulatory movements is also 



