618 SUMMARY OF CURRENT RESEARCHES RELATING TO 



(Anlage) ? 2. Why do not all leaves which are experimented upon 

 behave alike ? Finally, the author states that the likeness and differ- 

 ence between the different meristem plasmata cannot be explained ; that 

 they agree in all properties certainly, but that before the formation of 

 the respective organs of the plant a difference takes place in them. 

 Also that the meristem plasma of rhizome and rhizoid are more nearly 

 related than is either of these with the meristem plasma of the leaf. 



Periodicity in Dictyota at Naples.* — I. F. Lewis writes an interest- 

 ing account of the periodicity in the production of the sexual cells of 

 Dictyota dichotoma at Naples. Williams has described the same for 

 Bangor and Plymouth, and Hoyt for Beaufort, North Carolina. The 

 striking differences in the behaviour of the species in different localities 

 makes every fresh observation on the subject of importance. At Naples 

 the sexual cells of Dictyota were found to be produced at regular intervals, 

 the time of initiation of the rudiments and liberation of the mature 

 gametes bearing a definite relation to the periodic changes in the tides. 

 The crops are borne, as at Bangor, at fortnightly intervals. Initiation of 

 the rudiments occurs on the same day as general liberation of the mature 

 gametes, this being two or three days after the least neap tide. The 

 number of days required for the development of a single crop is approxi- 

 mately sixteen. The development of the sori is fairly uniform, not being 

 accelerated at the time of the spring tides. Charts of comparison are 

 given for the periodicity of plants at Bangor, Beaufort, and Naples. The 

 causes of periodicity are discussed. The author finds that Williams' 

 hypothesis, that the effective factor is the increased illumination during 

 low water of spring tides, is inadequate to explain the phenomenon at 

 Naples, since the Dictyota flourishes there at a depth of many feet below 

 the surface, and the difference between the height of low water at spring 

 and neap tides is only 0*25 foot. Nevertheless, he notes that the 

 critical points in the sexual life of Dictyota coincide exactly with the 

 periods of maximum intensity of illumination, both initiation and libera- 

 tion occurring at Naples on the day that low water occurs at or nearest 

 midday. The author believes that the stimulus of the maximum intensity 

 of light is only one of the factors in producing periodicity, and that the 

 factors may vary with the locality. Periodicity in the release of sexual 

 cells is a widespread phenomenon, probably to be attributed to various 

 factors in different species, and perhaps to more than one factor in the 

 same species in different localities. 



Himanthalia lorea.f — N. Wille has made a minute examination of 

 the anatomical structure of Himanthalia lorea, and gives a detailed 

 account of his results. The plant, as is well known, consists of a button- 

 shaped vegetative portion, and of long strap-shaped outgrowths which 

 bear the sexual organs. The vegetative part adheres to rocks at or near 

 low-tide mark, and lives for two or three years. In the second or third 

 summer of its life it produces the long strap-shaped thallus, which only 

 survives for one summer. Since the two portions of the plant are so 

 diverse in character, it follows that the anatomical structure is also 



* Bot. Gaz., 1. (1910) pp. 59-64. 



+ Jahrb. wiss. Bot., xlvii. (1910) pp. 495-538 (2 pis.). 



