1896. RECENT WORK ON SEAWEEDS. 39 



to form a layer of cells round the interior of the cystocarp. This 

 layer, he suggests, may possibly supply the mucilage which is found 

 in the mature cystocarp, and is afterwards ejected with the spores. 

 He notes other interesting details in other species of the Order. 

 There is a remarkable similarity among them in the structure of the 

 procarp at the moment of fertilisation, and only when spore-formation 

 has begun do they vary. 



Dr. Friedrich Oltmanns published in Pringsheim's Jahvbncher, 

 xxiii., 1891, an account of observations and experiments on the life- 

 conditions of Algae, all tending to prove the extreme sensitiveness of 

 these plants to change of environment. Temperature and illumination 

 had to be carefully attended to in any attempt to cultivate them ; but 

 the chief point of importance he decided to be variation in the 

 salinity of the water. Any abrupt alteration of density seemed to be 

 very hurtful, and he advocated careful and gradual change of water 

 in aquaria. Subsequent researches (14) have caused him considerably 

 to alter his opinion ; he found that the mortality in the weeds he was 

 dealing with was caused by undetected impurities in the water rather 

 than by any change of medium, though that, too, was not unimportant. 

 He was convinced that the oligodynamic effects described by Nageli as 

 being so fatal to Spivogyra cells had a potent influence on his plants. 

 In order to secure healthy growth, he had, therefore, to be very 

 careful to avoid using vessels made of metal to convey the sea- water. 

 The poverty of the flora at the mouths of canals and rivers, while 

 partly due, as he had supposed, to the constant alternation of fresh 

 and salt water, was also largely caused by impurities and by the 

 evolution of noxious gases due to decomposition. He was able to 

 change the water in which the weeds grew with a variation of ten per 

 cent, in salinity without the slightest effect on the plants. The best 

 results in culture were obtained by keeping up a continuous stream 

 of water through the aquarium, so gentle as not to carry off any 

 swarm-spores. Sterilising the water supplied was advisable, if not 

 necessary, to destroy bacteria and kill off all undesired spores. The 

 presence of carbon dioxide in larger or smaller quantities was not of 

 great importance within certain limits, so that the aeration of the water, 

 which Oltmanns had thought hurtful in carrying off too much of the 

 gas, had, in reality, no marked effects. One very interesting result was 

 the possibility of propagating algae by " cuttings." He grew a 

 quantity of Polysiphoniae and Ceramieae in this way, only he had to 

 see that each " cutting " of Cevamium included the small nodal cells, 

 otherwise the plant would not grow. 



Collectors of algae will be glad to learn that J. P. Lotsy describes 

 a simple method of preserving Red Algae, so as to keep the cells and 

 colour in their natural condition. The instructions are extracted 

 from the Botanischcs CcntralhlaU, vol. Ix., pp. 15, 16. " Place the 

 Algae in a solution of 10 grms. chrome-alum in i litre sea-water for 

 1-24 hours. Wash carefully to remove all trace of chrome-alum, 



