878 



SCIENCE 



[N. 8. Vol. XLII. No. 1094 



for the tree roots, well aerated, above the water 

 table. The Chaparral follows when the distance 

 to the water table becomes so great that the oaks 

 can not obtain sufficient water. The chaparral is 

 permanent because it flourishes independently of 

 moisture supply from the ground water. This 

 succession thus progresses from halophytic to 

 mesophytie conditions and from thence to xero- 

 phytic, the final stage being far less mesophytie 

 than the intermediate ones. 



In the mountain area successions are short and 

 indistinct and there will be no climax formation 

 for the whole area, short of base levelling. North 

 and south slopes will differ in vegetation as long 

 as they exist, the present dominant vegetation of 

 each aspect being the temporary climax of a short 

 succession. 



Discussion: Campbell, Clements, Eastwood. 

 The Flora of the Desert Basin of the Mohave: S. 



B. Parish, San Bernardino. 



The topography of the Mohave Desert is com- 

 plex in contrast with that of the Colorado Desert, 

 which is a simple valley, but the climatic and 

 edaphio conditions are practically identical, and 

 are of a pronounced xerophytic character, and 

 consequently such is the character of the plant 

 population. It is, however, locally modified by 

 intrusions through the passes; by the influence of 

 the Colorado Eiver and very markedly by that of 

 the Mohave River. The distribution of the cacti 

 is found to depend upon the amount and reliabil- 

 ity of the rainfall. Some account is given of the 

 vegetation in and about the infrequent springs. 

 Certain differences in the respective vegetations of 

 the Mohave and the Colorado Deserts are noticed 

 and shown to depend upon different emigration 

 currents. 



Friday, August 6, 10 A.M. 

 Some Features of the Distribution of the Marine 



AlgcB of the West Coast of North America: "W. 



A. Setchell, University of California. 



Discussion: Clements, Lawrence. 

 Gas Conditions in Nereocystis: T. C. Frye, Uni- 

 versity of Washington. 

 Physiological ConMtions in the Large Kelps of 



the Pacific Coast: G. B. Rigg, University of 



Washington. 



The great size and the rapid growth of the 

 four conspicuous kelps of the Pacific coast as 

 well as their potential value as a source of potash 

 fertilizer and of various by-products makes the 

 investigation of their physiological processes a 

 matter of both scientific interest and economic im- 

 portance. 



The growth of the large kelps Nereocystis leut- 



Jceana, Macrocystis pyrifera, Alaria fistulosa and 

 Pelagophycus porra is rapid. Possible factors in 

 this are (1) mechanical stretching by tidal cur- 

 rents (2) great turgidity due to high osmotic pres- 

 sure in cell sap (3) abundance of potassium, in- 

 fluencing nuclear division. 



There is much more potassium than sodium in 

 kelps while the reverse is true in sea water. Pos- 

 sible factors in this are (1) greater permeability 

 of the protoplasm for potassium; (2) a change of 

 potassium compounds into some other form which 

 does not lower the diffusion gradients. 



Workers are not agreed as to the source and 

 composition of the gases in the floats of marine 

 algfe, hence definite conclusions as to their part in 

 metabolism are impossible. 



Probably carbon dioxide for photosynthesis 

 comes from either the gas in these floats or from 

 carbonates in water, rather than from carbon di- 

 oxide in sea water. 



Tidal currents may be a factor in photosynthesis 

 by keeping the fronds at the surface. The kelps 

 produce no starch. Their sugars may be a fac- 

 tor in high osmotic pressure. 



Studies on the respiratory ratio in marine alga? 

 throw some light on the materials oxidized in res- 

 piration. 



This paper contributes (1) a summary of the 

 literature bearing on the physiological processes 

 in the large kelps; (2) some hitherto unpublished 

 data with regard to these processes; (3) some 

 suggestions as to possible interpretations of the 

 available data on them; (4) a statement of the 

 more conspicuous gaps in our information in re- 

 gard to these processes and of the importance of a 

 comprehensive investigation of them. 



The Personation and Multiplication of the Fruits 



of Certain Opuntias: D. S. Johnson, Johns 



Hopkins University. 



The fruits of some few of the cacti, like those 

 of certain Eucalyptoids, differ from those of most 

 other seed plants in not falling from the tree, at 

 the end of the growing season in which they were 

 initiated by the flower. In the exceptional forms 

 mentioned, of which Opuntia fulgida is one of the 

 most striking examples, the fruit remains at- 

 tached, and growing, season after season. 



The primary flowers of the season in Opuntia 

 fulgida are formed from the lateral buds, or 

 areolse, of the last year's branches and also from 

 areolse of the persistent fruits of former seasons. 

 These primary flowers shed the perianth five or 

 six days after the opening and give rise to fruits, 

 which not only remain attached but also give rise, 

 sometimes even before the flower has opened, to 



