560 SUMMARY OF CURRENT RESEARCHES RELATING TO 



a plant capable of transmitting its variegation by grafting. He finds 

 that if the leaves are removed from variegated plants, and the plants are 

 then kept in the dark, new shoots appear with only two or three 

 variegated leaves, and if the latter are removed the plant remains per- 

 manently green, unless infected afresh by grafting. If latent axillary 

 buds on old parts are forced into growth they produce variegated leaves, 

 which infect all the rest of the plant. If all variegated leaves are 

 removed and the plant exposed to light, it becomes permanently green. 

 Similar results were obtained with A. arboreum. The author believes 

 that the variegation is caused by a virus formed only in the light in the 

 affected parts of the plant ; also that this virus is formed only in small 

 quantities, which are quickly used up if the infected leaves are at once 

 removed. It is only able to infect embryonic leaves, and is then stored 

 for months in an inactive form. Experiments show that the virus, 

 moves in the cortex and not in the transpiration current. When 

 variegated A. Thomsoni is grafted with immune A. arboreum, the 

 scions grow well but are not infected, although if these scions are them- 

 selves grafted with a susceptible species, the virus passes through the 

 immune parts and infects the susceptible species. This virus may thus 

 be compared to the supposed shoot-forming substance of Sachs and the 

 growth-enzymes of Beijerinck. 



Starch in the Bryophyta.* — El. and Em. Marchal have carried out 

 a series of physiological researches on the presence of starch in hepatics 

 and mosses. In the first chapter they describe in detail their experiments 

 made upon some 50 hepatics and 90 mosses, to determine the existence 

 and localisation of starch in them. Their first list is systematic. For 

 convenience they then class the species in three groups according to 

 whether they contain much, little, or no starch. In the first group are 

 27 hepatics and 52 mosses ; in the second, 12 hepatics and 24 mosses ; 

 in the third, 11 hepatics and 14 mosses. Types of the first group, where 

 freshness is constant, are Cincinnulus trichomanis, Atrichum undulatuni; 

 types of the second group, exposed to short and rare periods of desic- 

 cation, are Lophocolea bidentata, Ceratodon purpureus ; types of the third 

 group, adapted to withstand prolonged desiccation, are Radula com- 

 planata and Neckera crispa. In the second chapter they consider the 

 effect of light, heat, water, and nutritive solutions upon the production 

 and fluctuation of the stores of starch, and find that the Muscineas react 

 in precisely the same way as do the chlorophyllose Phanerogams. 



Direction of Growth in Hepatics.f — B. Nemec has been studying 

 the direction of growth of the sporogonium and vegetative shoots of 

 certain hepatics in darkness both under the action of gravity and freed 

 from it. Varied results were obtained. The plants examined were 

 Lophocolea bidentata, Lejeunea serpyllifolia, Aneura pinyuis, Pellia caly- 

 cina, and P. epiphylla. Most of these were geotropic, and grew ortho- 

 tropically or plagiotropically upwards in the dark ; but the first two 

 species were ageotropic. 



* Bull. Soc. Roy. Bot. Belgique, xliii. (1906) pp. 115-214. 

 t Flora, xcvi. (1906) pp. 409-50 (9 figs.). 



