DEPARTMENT OF BOTANICAL RESEARCH. 65 



with Pcntstemon zvrighfii or beard-tongiie, a member of the Scrophulariaceae 

 which is native immediately around the Desert Laboratory. Ovaries were 

 injected with three reagents as noted above and the seeds germinated in the 

 autumn of 1907. Of the 60 individuals that came into bloom, 30 per cent de- 

 parted so far from the normal as to make the differences apparent even to the 

 novice. The atypic derivatives comprised 8 separate forms, one of which was 

 represented by 5 individuals and another by 4. Some of the departures were 

 very obvious retrogressive changes, consisting in the loss of structural char- 

 acters ; others showed the acquisition of characters not hitherto observed by 

 the investigator within the limits of the genus. This was particularly true of 

 a form in which the lobes of the corolla were conspicuously recurved. 



It is believed that a further study of this method may result in our ability to 

 modify the entire progeny of a plant, and furthermore to give these modifica- 

 tions definite trend or direction, by which man might control the evolution of 

 other organisms and produce relations among living things not now existent. 



Water Storage and Xeno-parasitism. — The investigation of the mechanism 

 of water-storage by succulents native to arid regions has engaged considerable 

 attention by Dr. MacDougal during the year with the attainment of some def- 

 inite progress. Some previous record has been made of the fact that many 

 storage plants carry a supply of water which would enable them to exist for a 

 quarter of a century without receiving further supplies. A number of tests 

 of other species, including several cacti, are being carried on to determine the 

 efficiency with which the specialization has been developed in various forms. 

 Of the results at hand those obtained from a great barrel-cactus (Echino- 

 cactus zvisliseni) may be mentioned. A well-grovv-n individual of medium 

 size, weighing 94 pounds in March, has been mounted on a base suitable for 

 weighing, by which it is seen to lose weight at the rate of about i pound avoir- 

 dupois per month, preserving, at the same time, a normal appearance. This 

 individual probably contains over 80 pounds of water, and it has endured tem- 

 peratures of over 100° F. for many days with the relative humidity as low as 

 6 per cent. (See plate 3.) 



The independence of entire individuals from a supply of water is also char- 

 acteristic of the branches or members of the body of many succulents. Thus, 

 the trunk of a great sahuaro (Cereus giganteiis) will decay as a result of dis- 

 ease and the bare woody brown column will be seen with a normal green 

 branch attached to it at a point 15 or 20 feet from the ground, in which posi- 

 tion it may receive nothing from the soil. 



In the effort to determine the physiological character of the storage tissues, 

 large preparations were made by which cuttings of various species were in- 

 serted in or in contact with the water-containing tissues of plants with special 

 mechanisms. Cactuses of various species were thus made parasitic on other 



