If we are to make any use of these measurements, it is uecessary that 

 all the Zostera shoots at a certain place should be almost the same in size and 

 leugtli ol' the leaves. On lookiug dowu upon the wavy field of grass-wraek in the 

 water, this supposition should seemingly be easy to fulfil; grass-wrack is very 

 much like a corn field in whieh the piants are generally almost equal in size, 

 and though the variations are large the numbers in the tables show that the 

 hypothesis is to some extent correct. It seems however that in tliis respect there 

 is some difference in the Zostera vegetation wheu growing in low water and on 

 hard bottora or in deep water and on soft bottom. 



Table II. 



Channel off Holckenhavn. 



Soft boltom, 24— 3J fathoms. 



In Table I the length of the lougest leaf of some shoots from low water 

 and hard bottom is given in cm. togetlier with the breadth of the leaf in mm. 

 The uumber of specimens (shoots) measured is rather variable and generally too 

 small, but unfortunately for practical reasous no more shoots were at my disposal, 

 partly because the collecting work had to be fairly easy to uudertake, partly be- 

 cause mauy of the leaves of the specimens sent were defective (the tips were 

 broken) rendering it impossible to decide which had been the longest. 



The measurements from August and September are however so uumerous, 

 that they show the extent of the variations, from which one can judge of the 

 vakie of the average. It appears from these that the variations are so consider- 

 able, that the average must be used with eaution and only as an approximate 

 number. The Table further shows that neither the numbers of the individual 

 measurements nor the averages vary in any certain direction, tliey rise and fall 

 (juite casually and after having studied the Table we can only say that the eel- 

 grass in low water and on hard bottom seems rather invariable in tlie 

 course of the year as regards the length of leaves. The breadth of the 

 leaves only shows slight variations, such as from 2,5 to 4,5 mm., and is also uuin- 

 fluenced by the time of j'ear. 



