79 
Nachet’s and other Immersion Lenses A correspondent 
wishes for the opinion of the readers of the Journal on the 
comparative merits of immersion and other lenses, for various 
forms of work. We shall be happy to insert any remarks 
upon the subject, based on experience. 
Cell Diagnosis — We are anxious to suggest to those who 
have the time the importance of a series of observations on 
the various forms of tissue, the hairs, pollen-grains, raphides, 
and starch-granules of plants. Any observer who will care- 
fully examine a genus at a time, in these respects, as Mr. 
Gulliver has done qu& Raphides, would perform valuable 
work. We should be pleased to publish a series of such 
papers. 
Pain. — Some time ago a very small quantity of a fine silky 
substance w r as brought to England from California under 
the above name, and it was used as an object for the 
microscope, on account of its beautiful structure. Mr. Bing- 
ham, in his very interesting paper on the “Volcanic Pheno- 
mena of the Hawaiian Islands,” says — “ Palu is the silky 
covering of the opening fronds of several species of tree ferns, 
and is exported in large quantities to California, for beds, 
&c.” (p. 4:26). The trade is so extensive that “ corduroy 
roads” are made to the station where it is collected, and 
■whole districts are leased for the “ Palu business,” and there 
is a large number of “ Pa/w-pickers.” The Palu is collected 
at Kelauea, which is the most tropical region in Hawaiia ; 
the tree ferns have stems fifteen feet high to the base of the 
frond, and eight or twelve inches in diameter. 
