HOWIETOUN PLANK PONDS. 



155 



was raised by a screw, thus securing great nicety in the quantity of 

 water passed. The sluice was always set so as to dam the water 

 against the screen, and secure a certain overflow, as the stream 

 often carried gravel on to the screen, and it was necessary to keep 



-- a'. 3 



FIG. 116 scale -fa. 



a good flow over it to clear it ; now all water is taken from a 

 damhead, and gravel is no longer a source of trouble. 



THE PLANK POND 



was built to succeed the rearing-box, and it has supplanted it 

 entirely. To-day the rearing-boxes exist, nay, they are numerous, 

 under a different name, but they are no longer used as rearing- 

 boxes. They have been found most useful in preparing trout 

 for long journeys, yearling fish especially; but fry no longer 

 require them. When the great fact was realised that eggs should 

 be hatched where the alevins are to spend the first two or three 

 months of their existence, be it in redds or hatching-troughs, 

 rearing-boxes, as rearing-boxes, became a thing of the past. 

 Now that two-year-olds are the fashionable size for stocking, 

 plank ponds as rearing-ponds bid fair to follow. Plank ponds are 

 the best suited for the preparation of two-year-olds; but in 1875 

 I knew nothing of the art (for it is a very great art indeed) of 



