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SCIENCE 



[N. S. Vol. XXV. No. 634 



responding increment of loss from an 

 evaporimeter for the same interval, the 

 paper proceeds to present a new fact in 

 regard to the regulation of transpiration. 

 While ordinary leafy plants in some way 

 retard water-loss during the hours of dark- 

 ness and remove the retarding influence 

 during those of light, the cacti, at least as 

 far as the study has gone, act in a manner 

 exactly opposite, applying the retarding in- 

 fluence during the daylight hours and re- 

 moving it during those of darkness. Thus, 

 for a given transpiring surface, leafy 

 plants lose water in the daytime more 

 nearly at the rate of the same area of free 

 water surface than they do at night, and 

 cacti more nearly approach the evaporation 

 rate from a water surface during the night 

 than in the daytime. Data as to the na- 

 ture of the mechanism by which either 

 group of plants accomplish their regula- 

 tion of water-loss is as yet entirely lack- 

 ing, since Lloyd, in a paper about to be 

 published, has thrown great doubt on the 

 usually accepted idea that this regulation 

 is mainly accomplished through stomatal 

 movements. 



The Water-Storing Tubers of Nephrolepis 

 cordifolia: Professor J. W. Haksh- 

 BERGER, University of Pennsylvania. 

 Nephrolepis cordifolia is a fern occa- 

 sionally met in cultivation. When grown 

 in the open it forms tubers the size of a 

 walnut. These are developed at the end 

 of lateral underground branches covered 

 with flat, scale-like ramentse which extend 

 also to the surface of the tuber. The 

 tubers do not store starch and other reserve 

 foods, as an external examination of the 

 tubers might lead one to expect, but the 

 large, rounded, parenchyma cells are 

 turgescent with a clear watery fluid, evi- 

 dently stored against the time of drought, 

 as the fern is usually epiphytic in habit. 



When these tubers are dried, they dry until 

 they almost entirely shrivel up. 



A New Native Host for Pearilight: M. B. 



Waite, Bureau of Plant Industry. 



The pearblight bacillus, B. amylovorus, 

 is undoubtedly a native parasite on the 

 American indigenous species of Pomacese; 

 it occurs nowhere else in the world and is 

 quite commonly found on the wild crab- 

 apples and hawthorns of the eastern United 

 States. 



When pears and apples and other 

 pomaeeous fruits were introduced into this 

 country it promptly attacked them. It is 

 quite easy to find new hosts on cultivated 

 species of the Pomacese, as almost every- 

 thing belonging to this family when grown 

 within the territory affected is likely to 

 be attacked. Some of these Pomacese look 

 very unlike our ordinary pears and apples, 

 but, nevertheless, may be subject to this 

 disease, e. g., the evergreen Eriobotrys 

 Japonica is attacked by this disease very 

 commonly in Florida and Georgia, and re- 

 cently has been found affected in Cali- 

 fornia. The arid plains and deserts and 

 the Rocky Mountain region appear to have 

 formed an insurmountable barrier, deter- 

 mining the western limits of the pearblight 

 germ. Within the last few years, however, 

 doubtless through human agencies, the 

 pearblight bacillus has jumped, first to 

 Colorado, Utah, Idaho, etc., and finally 

 over the deserts and the Sierras into Cali- 

 fornia. It is now attacking with unusual 

 virulence the pear orchards of that state. 



Few native Pomaceae occur in California 

 in the vicinity of the pear orchards. The 

 beautiful, red-berried, California holly, 

 Heteromeles arbutifolia Eoem., is, however, 

 quite common in the foot-hills of the 

 Sierras, in the coast ranges, and comes 

 down into the fruit regions. This shrub 

 with its thick evergreen leaves looks very 

 much unlike a pomaeeous fruit, but was 



