THOMAS HOPKIRK OF DALBETH. 203 



lock is 156 feet above the first one. This level is 

 maintained for 16 miles. From the twenty-first lock 

 at Maryhill to the thirty-ninth lock in Bowling 

 Bay, there is again a descent of 156 feet, and that 

 in 8| miles. Thus for about 15 miles east of Fossil 

 there is an open canal, while about a mile to the 

 west the locks begin. This would appear to be 

 more favourable to the introduction into the marsh 

 of plants from the East than from the West. 



Again, the cutting of the canal was commenced 

 in 1768 from the East side, and in 1775 it was open 

 to a point nearer Glasgow than the marsh. In 1790 

 it was open to Bowling, that is, from sea to sea. 

 We thus perceive that the marsh had an Eastern 

 connection for many years before the Western one 

 was completed. 



We can hardly doubt that both of these circum- 

 stances, alike in favour of the introduction of plants 

 from the Eastern district, have had some influence 

 on the flora that now inhabits it; but as we can- 

 not say how much the whole character of the 

 vegetation may have been affected by the canal, so 

 do we remain at a loss to determine the effect of 

 these causes. It has little bearing on the subject 

 that the vegetation of the marsh does not now 

 show many indications of change. It has been fre- 

 quently observed that a sudden alteration in con- 

 ditions like this introduces new forms of vegetation 

 for a time till comparative stability is again attained. 



Tlie Mare's-tail, for instance, had probably not 

 reached the marsh in 1813, and certainly had not 

 succeeded in developing there in any quantity, as it 

 is quite inconceivable that Hopkirk or any other 

 botanist could have overlooked so conspicuous a 

 plant, if it had occurred in anything approaching 

 the profusion now attained. 



Ctrccea lutetiana he mentions as *' in shady places 

 and woods occasionally," giving a few stations. 

 Patrick and Kennedy both record it as frequent, 

 and when we recollect how often we have found it 



