ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 59 



Regeneration and Polarity in Higher Plants.* — H. Vochting has 

 investigated the cause of polarity in higher plants. Experiments on 

 Mercurialis annua show that the seeds of plants grown on a klinostat 

 produce seedlings which are indistinguishable from those arising from 

 seeds grown under normal conditions. A. second series of experiments 

 was performed upon Lopezia coronafa. Some of the plants were placed 

 on the klinostat in a horizontal position, others in a vertical position, 

 and a third set in a position midway between the horizontal and vertical. 

 As before, the seedlings were normal. These seedhngs were then grown 

 on the klinostat, and cuttings were taken from them ; some cuttings 

 were planted in an upright position, while others were inverted. The 

 former developed a few roots at their base, but the latter only produced 

 a callus and soon died. The author concludes that polarity is not 

 induced through the influence of any external force, but is a property of 

 the plant tissues, which exists from the first, in the fabric of the 

 idioplasm of the egg-cell. 



Desert Shrubs and Atmospheric Moisture .f — V. M. Spalding has 

 experimented with desert plants with the object of ascertaining if the 

 leaves are capable of absorbing atmospheric moisture. The author finds 

 that in Fouquieria s]}Uiidens the leaves are incapable of absorbing water, 

 but that a moist atmosphere tends to suppress transpiration, which is 

 probably the reason for the retention of leaves in a moist atmosphere. 

 Leafless shoots are able to absorb considerable quantities of water- vapour 

 from a saturated atmosphere, but the rapidity with which they give it 

 out again, even when the relative humidity is high, seems opposed to 

 the view that much moisture is received from this source. Similar 

 results were obtained with other types. 



Physiology of Diatoms. i — 0. Richter describes the result of his 

 experiments on the physiology of diatoms. Some years ago he discovered 

 a method of ensuring pure cultures of these organisms, and he is there- 

 fore able to be sure of his facts. He finds that Nltzschia 'palea W. Sm. 

 cannot live without silicic acid in the form of CaSiaOg or K2Si205. It 

 is probable that calcium is also necessary, at least when SiOa is offered 

 in the form of Ka^i-iOs- Navkula minuscula has a still stronger need 

 for chalk, while magnesium is another necessary ingredient in the food 

 material of both species. Both are able to assimilate organic com- 

 pounds of nitrogen, most easily asparagin and leucin, whereas in a free 

 state nitrogen is useless to them. On the whole, diatoms need a weak 

 alkaline reaction. The effect of other compounds is given, as well as the 

 result of experiments in the degree of light and darkness most favourable 

 to growth. The two species were found to be positively phototactic. 



Irritability. 



Galvanotropism of Roots.§— G. (lassner has investigated the effects 

 of electric currents upon roots, and finds that (other conditions being 



* Bot. Zeit., Ixiv. (1906) pp. 101-48 ( 3 pis.), 



t Bull. Torrey Bot. Club, xxxiii. (1906) pp. 367-75. 



X SB. k. Akad. Wiss. Wien, cxv. (1906) p. 935 (6 pis.). 



§ Bot. Zeit., Ixiv. (1906) pp. 149-222 (11 figs.). 



