ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 67 



kept systematic records of the details of variation from 1897 to the 

 present time. He finds that the crops of sexual cells are initiated, 

 matured, and discharged in the space of a fortnight, and that a general 

 liberation of oospheres and antherozoids takes place on a certain day, 

 sometimes two or three days immediately after the highest spring tide. 

 Deviations from this rule occur, however, and the causes of such 

 deviations are discussed in the present paper. The author first proceeds 

 to give a general description of the sexual plant. D. dichotoma is an 

 annual, and the germling commences to elongate during May. Fruiting 

 plants may be met with in June, but reproduction is not common till 

 the end of July. During August and September periodicity is regular, 

 and after that it slows down, and ceases towards the end of November. 

 The antheridia and oogonia are, as stated above, produced in fort- 

 nightly crops which synchronise with the spring tides, and the develop- 

 ment of the crops is determined by the time and height of these tides, 

 progress being very slow during the neaps. The causes which produce 

 this periodicity are variations in the degree of aeration and of pressure, 

 and particularly differences of temperature and of illumination. The 

 author has examined and watched the development of D. dichotoma both 

 in the Menai Straits and at Plymouth, and he finds that the difference 

 between the details of periodicity at these two places is due to the 

 difference in the time of day at which low water of spring tides occurs 

 in the two places. In the Menai Straits the time of lowest water falls 

 in the hours of daylight during the summer months, while at Plymouth 

 it occurs at midday and midnight. Thus at Plymouth the total amount 

 of light obtained during spring tides is less, and the result is that the 

 plants are poorer and the crops are several tides later in their develop- 

 ment. Thus periodicity is seen to be affected by illumination, and 

 since winds may affect the tide and cause a difference of level, they may 

 also be regarded as factors in the question. The author finds that in 

 herbarium specimens from the Southern hemisphere periodicity may be 

 traced, but only in localities where there is an appreciable change of 

 tide level. Finally, suggestions are made of the lines along which 

 future work on the subject should be carried out. 



Anderson, J. P. — Decatur County Algae. Iowa Nat., i. (1905) pp. 55-8. 



Anonym ou s — Fresh-water Plankton. (Continued.) 

 [Article in Japanese ; names in Latin.] 



Bot. Mag. Tokyo, xix. (1905) No. 220, pp. 66-9, 106-8. 



Bettels, J.— Die Kohlehydrate der Meeresalgen und daraus Hergestellte Erzeu- 

 gnisse. (The carbohydrates of marine algse and their derivatives.) 



Dissert. Hildesheim, 1905, 54 pp. 



B o e b a s, V. v. — Planktontelep O-Buda vizeiben. (A plankton station in the O-Buda 

 waters.) 



[The author finds free-floating Lemna plants chained together by filament- 

 ous algse.] Magyar Bot. Lapok, ii. (1903) p. 195. 



C a s u, A. — Contribuzione alio studio della flora delle saline di Cagliari. (Contribu- 

 tion to the study of the flora of the saltworks of Cagliari.) 



[Mention is made of Microcoleus chthonoplastes Thur. studied by Cavara in 

 1902.] Ann. de Bot., ii. (1905) pp. 403-33 (2 pis.) 



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