THE DREAM FULFILLED 153 



markable discovery relating to the formation of pearls 

 in the river Pearl Mussel l not to be confounded with 

 mother-o'-pearl. 2 The former is found in rivers, in 

 all the northern parts of the world Sweden, Ireland, 

 England, Scotland. From observations on the growth 

 of the shell of this animal, and the number of its 

 laminae, or scales, fifty or sixty years are thought to 

 be a moderate computation of its duration of life. 

 Linngeus discovered a method of putting these mussels 

 into a state of producing pearls at his pleasure, though 

 the final effect did not take place for several years. 

 He says that in five or six years the pearl would have 

 acquired the size of a vetch. 3 Most likely this was 

 effected by injuring the shell externally, perhaps by a 

 perforation ; for it has been observed that these concre- 

 tions in shells are found in the' inside exactly opposite 

 to perforations and injuries made by serpulae and other 

 animals. 



On May 21, 1743, Professor Roberg died, when 

 Linnaeus obtained the whole salary of his office, having 

 up to this time enjoyed nothing but his pension. 4 



The Swedish Government honoured Linnaeus highly, 

 and built him a house at the entrance of the botanical 

 garden, of which beautiful premises (the house and 

 private garden) he took possession on July 18, 1743. 

 This raises the question, Is this the plain small house at 

 the corner of the Svartbacksgatan, No. 2 7, which tradi- 

 tion and a slab in the wall point out as the residence of 

 1 Mya margaritifera. 2 Seashell. s Pulteney. 4 Stoever. 



