326 



SCIENCE 



[N. S. Vol. XLIII. No. 1105 



ranges. The boundary between the patanas and 

 the adjoining forests is remarkably sharp. The 

 origin of the patanas is obscure, but their per- 

 petuation is due entirely to the fires which sweep 

 over them annually. Near plantations where the 

 fires are excluded, a thicket association, character- 

 ized by BJiododendron arboreum and Sypericum 

 mysorense, develops immediately, and is followed 

 by the regular subalpine forest. 

 Ohservations on the Sevegetation of the Katmai 



District of AlasTca: Robert F. Griggs. 



Under the auspices of the National Geographic 

 Society the author has undertaken the investiga- 

 tion of the return of vegetation to the country 

 devastated by the eruption of Mt. Katmai in 1912. 

 Where the deposit of ash did not exceed one foot 

 in depth, as, for example, at Kodiak, vegetation has 

 made a most surprising recovery so that the grass 

 and berries for which the district is famous, are 

 finer than ever before. The new growth, however, 

 is made up exclusively of surviving plants. Where 

 for any reason the original plants did not persist 

 the ground is nearly always as bare as when the 

 ash first fell. Except in sheltered situations the 

 ash is picked up by the wind, giving rise to a 

 severe sand blast and forming great dunes which 

 give little opportunity for the start of new seed- 

 lings. In more sheltered situations seedlings have 

 started, but as yet form no important element in the 

 vegetation, for their growth is very slow. Near 

 the volcano the deposits were deeper; almost all 

 vegetation was destroyed, leaving the country a 

 bare desert. But some of the herbage persisted in 

 sheltered nooks where the ash was quickly washed 

 off the surface before the plants were suffocated. 

 Such oases are, however, entirely insignificant in 

 the barren landscape. Except for sporadic acci- 

 dental instances, revegetation has not yet begun 

 on the mainland. 

 The Cactus Columns of the Bad Lands: Raymond 



J. Pool. 



Few cases are on record of cactus species serv- 

 ing as soil binders in opposition to the erosive 

 forces of the environment. It appears that the 

 root systems of cactuses are mostly characterized 

 by the presence of shallow but more or less exten- 

 sively spreading horizontal roots. Such plants are 

 ordinarily rather easily uprooted. However, sev- 

 eral instances have been noted in the Bad Lands 

 of northwestern Nebraska of certain species of 

 Opuntia which have a root system considerably 

 deeper and less widely spreading than most cactus 

 species. Furthermore, cushions or colonies of this 



species resist erosion to a surprising degree. The 

 soil surrounding such cushions has been weathered 

 away, leaving erect columns of the soil capped by 

 the closely aggregated cushions or colonies of the 

 cactus. These columns are sometimes more than 

 ten feet high and vary in diameter from two feet 

 to ten feet. 



Modern Changes in the Prairie Groves of Iowa: 



B. Shimek. 



It is often asserted that since the cessation of 

 prairie fires the groves in the prairie region, in- 

 cluding Iowa, have extended beyond their earlier 

 limits. So far as Iowa, at least, is concerned, this 

 is disproved by the testimony of old settlers, but 

 especially by the records of the original govern- 

 ment surveys. Several specific cases are presented 

 in detail and illustrated by maps. The condition 

 of the prairie groves is discussed with special ref- 

 erence to changes of an ecological character which 

 are taking place and in which fire has played an 

 unimportant part. The most marked change which 

 is noticed is the increased density of both forest 

 and undergrowth in the undisturbed groves. Inci- 

 dentally this weakens or destroys one of the 

 strongest supports of the view that fires caused the 

 treelessness of the prairies. The results achieved 

 in artificial tree-planting are also discussed. 



Illustrating the PricMy Pears and Their Allies: 



David Gkippiths. 



In connection with the investigation of cactus 

 conducted by the U. S. Department of Agriculture, 

 distinguishing records of the species and varieties 

 handled soon became imperative. In a group 

 whose vegetative characters have in the past been 

 relied upon mainly for taxonomic purposes, the 

 task of distinguishing and depicting accurately the 

 species dealt with in field tests and breeding in- 

 vestigations has been decidedly difficult. Some 

 years ago it was decided to illustrate the species as 

 accurately as possible. A living collection of 

 2,400 numbers of Opuntia has been accumulated 

 at Chico, California. These are grown under field 

 and sash house conditions and at present form the 

 basis of the work. Characteristic portions of the 

 plants, i. e., old and young joints, flowers, buds 

 and fruits are photographed to scale. Where the 

 objects are large and the details complicated, as 

 in the case of the joints, these photographs are 

 used as a base for the water-color painting. In 

 the case of fruits and buds, especially, they are 

 outlined by the use of a camera luoida adapted to 

 macroscopic work. Every effort is made to pre- 



