No. 390.] REVIEWS OF RECENT LITERATURE. 543 
brilliantly colored, browns, grays, and yellows preponderating. They 
are very rich in variety of forms, but these seldom resemble the 
separate growths of either component. Nearly 20,000 species, varie- 
ties or forms of lichens, have been described, but only about 4000 
are well known. Lichenes are distributed over the whole earth. 
They occur farthest north and farthest south, and highest up on 
mountains of any plants. They are resistant to heat and to cold. 
Hot countries are relatively poor in species. In the Torrid zone 
they are found mostly on trees. The outer fungus rind is thin in the 
shade and thick in the sun. In hot, dry countries all the lichens 
have a common habit (Australia, Cape of Good Hope, Chili). Cold 
countries, especially in the northern hemisphere, are richest in spe- 
cies. Many species are widely distributed. Very few are edible. 
Among the latter, perhaps the most interesting is the rapidly growing 
manna lichen, known to the Tartars as earth bread, and a variety of 
which (Lecanora esculenta var. jussufit), easily blown about by the 
wind, and then known as “rain manna,” is perhaps the manna of 
the Israelites. Erwin F. SMITH. 
Agardh’s Algæ.'— It is not often that an author, fifty years after 
the issue of the first part of a work, is, like Professor Agardh, still 
continuing its publication. Nor does this fifty years by any means 
cover the time during which the name of Agardh has been among 
the foremost in algological science. The elder Agardh, father of the 
present author, was already publishing his observations quite early 
in the present century, and in 1823 he issued the first volume of his 
Species Algarum, intending to include in the work all the species 
known at the time. It remained unfinished, but it marks a distinct 
advance in systematic algology. 
Its author had the valuable faculty, in arranging a genus or group 
of higher rank, of seeing clearly the really distinctive characters and 
using them as a basis of classification. This faculty appears in even 
a higher degree in his son, J. G. Agardh, and for many years his 
Species Algarum, of which the first volume was published in 1848, 
has been the standard, especially as to the red alge. It is only 
within the last three or four years that an arrangement of the red 
alge, differing seriously from Agardh’s, has been presented and has 
met with any general acceptance. The arrangement of Schmitz, as 
given by Engler and Prantl, is based on the details of the fertilization 
1 Agardh, J. G. Species, Genera, et Ordines Algarum, voluminis tertii, pars 
tertia. De dispositione Delesseriearum curae posteriores. Lund, 1898. 
