ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 603 



by perennial stem-bases. The second type, represented by S. lonf/i/ie* 

 and S. umbellata, persists by " hibernating buds above ground and by 

 subterranean stolons." This type is very characteristic of plants 

 subject to extreme climatic conditions. The third type, represented by 

 8. Jamesii, has a well-developed rhizome, but the aerial stems are annual. 

 The rhizome is much swollen, and bears membranous, scale-like leaves ; 

 only those buds which are near the apex develop into aerial, floral shoots, 

 other buds remain dormant. The third type appears to be rare in the 

 Caryophyllaceae. 



Physiology. 

 Nutrition and Growth. 



Transpiration.* — G. L. Clapp has studied transpiration with the 

 view of discovering what plants are most suitable for purposes of class- 

 demonstration. The results obtained are recorded in a series of graphs, 

 which bring out the following facts. Transpiration is at its maximum 

 when sunlight is most intense, moisture is least, and there is a good 

 supply of water in the soil. The minimum is reached when temperature 

 is low, atmospheric moisture is near the point of saturation, and dark- 

 ness is complete. Transpiration is extremely sensitive to slight changes 

 in external conditions, and points to the possibility that the relation 

 between such conditions and the amount of vapour given off is not 

 purely physical, but " involves the action of the conditions as stimuli." 

 Of the plants examined, Helianthus annum transpires most, but is un- 

 suitable for class-demonstration. Among those most suitable for such 

 purposes are TropcRoluni majus, Pelargonium domesticum, and Fuchsia 

 speciosa. The average amount of transpiration for ordinary green-house 

 plants is 50 grin, per hour per square metre of surface in daylight, and 

 10 grm. in night-time. 



Irritability. 



Geotropic Sensibility of the Root.f — Gr. Haberlandt has investi- 

 gated the statements of A. Piccards as to the geotropic sensibility of 

 the root. Having repeated the experiments made by this investigator, 

 the present writer is led to agree with bis conclusions, which are briefly 

 as follows : Ttie geotropic sensibility of the root extends from the root- 

 tip to the zone of growth, but is greater in the tip, especially at a 

 distance of 1*5 to 2 mm. from the end. This greater sensibility of the 

 root-tip corresponds to the larger number of statoliths in the root-cap. 

 The sensibility in the zone of growth is clue to the statoliths of the 

 periblem. Usually the statoliths are deposited irregularly, but in the 

 zone of most rapid growth in Vicia Fdba they are in layers. By the appli- 

 cation of a sufficiently great centrifugal force, the position of the stato- 

 liths in relation to the cell-walls may be changed, and the response to 

 the force of gravity overcome. All the experiments performed favour 

 the Statolith Theory. 



* Bot. Gaz., xlv. (1908) pp. 254-67 (-2 figs., 30 graphs). 

 f Jahrb. wiss. Bot., xlv. (1908) pp. 575-600 (2 figs.). 



