536 Floristik, Geographie, Systematik etc. 



hold og Udbredelse i vore Farvande. English edition: On 

 the Ecology and Distribution of the Grass-wrack {Zostera 

 marina) in Danish waters. (Translated from Fiskeriberetning 

 for 1907. Rep. of the Danish biological Station. XVI. Copenhagen 

 1908. PI. 1—62. 8 figures.) 



The author gives a description of the structure and growth 

 of Zostera. The leaves appearing to have no resting-period, it has 

 been a difficult task to find out how the plant grows and how many 

 leaves are produced in the course of a year. By aid of a long series 

 of measurements it has been found that in deep water and on soft 

 bottom the leaves are much longer in summer than in winter and 

 spring, and that the oldest leaf (the outermost) is the longest 

 throughout the autumn and winter, whereas in mid-summer the 

 second, the third, fourth or even the fifth outermost leaf is the lon- 

 gest. Hence it can be supposed that Zostera produces yearly 4 to 

 6 new leaves on each shoot, 



Behind the leaves, each shoot has some sheaths which have 

 lost their blades. It is characteristic that the blades are thrown off 

 at their base, whereas the sheaths remain for a long time and only 

 gradually decay. The largest quantity of leaves are thrown off du- 

 ring the autumn, and in this season loose leaves of Zostera are 

 found floating about in the sea in quantities and is partly washed 

 ashore, partly sinks to the bottom, forming „dead-weed". 



The Grass-wrack can only grow in saline water, but it is not 

 particular about the degree of salinity, its distribution in the Baltic 



extending as long as to the Aland Sea, where the salinity is only 

 about 0,6 per cent. 



A sheltered locality is another condition, Zostera cannot grow 

 where the waves beat heavily, and therefore the open west coast 

 of Jutland is nearly devoid of it. 



As to the light, Zostera goes deepest down in the open waters 

 where the water is transparent, and to a less depth in the muddy 

 waters in the fjords. As a whole, Zostera never goes farther down 

 than 6 fathoms (ca. 11 m.). 



The nature of the bottom soil influences the growth of Zostera 

 in that manner that plants growing on firm sand have comparatively 

 Short and narrow leaves and a strong root-stock, whereas the Mud- 

 Zostera has long and broad leaves, reaching sometimes a length of 

 240 cm. and a breath of 5—8 mm. In contradiction to other authors 

 it is stated that the size of Zostera is more dependent on the 

 nature of the bottom soil than on the depth in which it grows. 



On stony soil, Zostera is often mixed with brown and red algas, 

 and in brackish water especially with green algae — the fauna of 

 the Zostera Vegetation is here briefly mentioned. 



A special chapter is consecrated to short descriptions of the 

 other marine flowering plants, vfz. Zostera nana, Riippia maritima , 

 Zanichellia palustris and Fotamogeton pectinatus. 



The distribution in danish waters of all species, but especially 

 of Zostera marina, is given in details and partly mapped. 



Ove Paulsen. 



Peck, C. H., Report of the State Botanist 1907. (Museum Bull. 

 CXXII. N. Y. State Museum. Albany, N. Y. Aug. 15. 1908. = Edu- 

 cation Department Bulletin 429.) 



An octavo of 175 pages, with 5 plates: including three special 



