XXVI SUMMARY. PHYSIOGNOMY OF PLANTS. 



p. 266. The indurating crust of the earth while giving out caloric. 

 Heated currents of air, which in the primordial period, during the fre- 

 quent corrugations of the mountainous strata, and the upheaval of 

 lands, have poured into the atmosphere through temporary fissures 

 and chasms — pp. 266-268. 



Colossal size and great age of certain genera of trees, e. g., the 

 dragon-tree of Orotava of 13, the Adansonia digitata (Baobab) of 33 

 feet in diameter. Carved characters of the 15th century. Adanson 

 assigns to certain Baobab-stems of Senegambia an age of from 5000 to 

 6000 years— pp. 268-273. 



According to an estimate based on the number of the annual rings, 

 there are yews (Taxus baccata) of from 2600 to 3000 years old. Whether 

 in the temperate northern zone that part of a tree which faces the north 

 has narrower rings, as Michael Montaigne asserted in 1581? Gigantic 

 trees, of which some individuals attain a diameter of above 20 feet and 

 an age of several centuries, belong to the most opposite natural families 

 —pp. 273-274. 



Diameter of the Mexican Schubertia disticha of Santa Maria del Tule 

 43, of the oak near Saintes (Dep. de la Charente inf.) 30 feet. The 

 age of this oak considered by its annual rings to be from 1800 to 2000 

 years. The main stem of the rose-tree (27 feet high) at the crypt of 

 the church of Hildesheim is 800 years old. A species of fucus, Macro- 

 cystis pyrifera, attains a length of more than 350 feet, and therefore 

 exceeds all the conifera in length, not excepting the Sequoia gigantea 

 itself— pp. 274-276. 



Investigations into the supposed number of the phanerogamic species 

 of plants, which have hitherto been described or are preserved in herba- 

 riums. Numerical ratios of plant-forms. Discovered laws of the geogra- 

 phical distribution of the families. Ratios of the great divisions : of the 

 Cryptogamia to the Cotyledons, and of the Monocotyledons to the Dicoty- 

 ledons, in the torrid, temperate, and frigid zones. Outlines of arith- 

 metical botany. Number of the individuals, predominance of social 

 plants. The forms of organic beings stand in mutual dependence on 

 each other. If once the number of species in one of the great families 

 of the Glumacese, Leguminosse, or Composite, on any one point of the 

 earth, be known, an approximative conclusion may be arrived at not 

 only as to the number of all the phanerogamia, but also of the species 

 of all remaining plant-families growing there. Connection of the 

 numerical ratios here treated on in the geographical distribution of the 

 families, with the direction of the isothermal lines. Primitive mystery 

 in the distribution of types. Absence of Roses in the southern, and of 

 Calceolarias in the northern zone. Why has our heath (Calluna vul- 

 garis), and why have our Oaks not progressed eastwards across the Ural 

 into Asia? The vegetation-cycle of each species requires a certain 

 minimum heat for its due organic development — pp. 273-287. 



Analogy with the numeric laws in the distribution of animal forms. 

 If more than 35,000 species of phanerogamia are now cultivated in 



