21 



of protection (see p. 17) — we find^) that the pure firm saud reaches a depth of 

 about 7 fathoms, after which follows a »mixed« soil, which again passes over into 

 the pure clay bottom (ooze) at a depth of about 20 fathoms. It is thus only the 

 pure saud bottom which comes into consideration for the grass-wrack, and it grows 

 on this in scattered piaces in the part of the Kattegat which is generally called 

 Aalborg Bay, namely, the shallow water bouuded to the north by Læsø, to 

 the west and south west by the east coast of Jutland (Djursland), and to the 

 south-east by Anholt; and it forms f urther an almost unbroken border aloug 

 the coast from i/., — 1 fathoms depth and to a depth of 5 — G fathoms. It is more 

 rare in quite shallow water, possibly because the waves beat too heavily there, for 

 we find it immediately there is any protection or shelter. C. G. Joh. Petersen 

 and I. Chr. L. Levinsen (Beretning fra den danske Biologiske Station IX, 1900, 

 p. 32) say regarding the northern part of the Kattegat: »The Zostera is able to 

 take root already at a depth of 1 

 fathom«; the upper limit is thus 

 placed here at a depth of 1 fathom. 



The grass-wrack found on 

 firm sand like this has the same 

 appearance, whether it grows at a 

 depth of 1 fathom or of nearly 

 6 fathoms. The leaves are com- 

 paratively short and narrow, the 

 creeping root-stock is strong, with 

 often rather long internodes; tiie 

 flowering shoots can be seen now 

 and then, although not as often as 

 in the bays. 



The accompanying figure 

 is a reduced representation of the 

 Kattegat-Zostera and should be 

 compared with the figures (figs. 1 

 and 6) of Mud-Zostera. In the Table 

 of measuremeuts (pp. 41 — 45) are 

 given the length of the leaves, the 

 leugth of the sheaths, the breadtli 

 of the leaves and the length of the 

 flowei'ing shoots. It is evident from 

 these that the length of the leaves 

 only rarely reaches 100 cm., and 

 the breadth varies between 3 and 

 5 mm.; the flowering shoots on the 

 other band mav reach quite 150 cm. 



r^, ' , ,1 ^ Fi" 3 I.cafbearing {A) and flower-bearing (B) shools of the 



The grass-wrack on the firm Kattegat-zostera. 



bottom in tlie Open Baltic has quite (Fim. san.ly bottom; OstreFlak, s. of Læso, .=) fm. 25. VI!. 01). 



') Beretning fra (U'u ilanske Biologiske Station IX, 1900. 



:rJ 



