THE PlyANT WORI.D 159 



ceous character. Those parts of the stem, therefore, which would be 

 unable to withstand the cold of winter are removed. In many plants 

 the flowering shoots are removed in a similar manner, as an example of 

 which we may note the shedding of the staminate catkins of poplars. 



Another very instructive instance is that of Fouquieria Macdougalii, 

 one of that group of curious desert shrubs called by the Mexicans 

 "ocotillo." The behavior of this plant has been recently described by 

 Miss Winifred T. Robinson,* and is briefly as follows. 



Within the petiole of the leaf, in the cortex of the under side, a strand 

 of hard mechanical tissue is formed, the development of which is begun in 

 the bud. This is accompanied by the differentiation of a separation-layer, 

 placed longitudinally in the petiole, between the mechanical tissue and 

 the outer layers of cortex. So far as known, this is the only genus in 

 which a separation-layer is so placed. On the approach of drought or 

 the cold .season, the leaf-blade is cast off, leaving behind a spine which 

 has been previously formed. In this unique waj^ the ' ' ocotillo ' ' conforms 

 to the spinose type of desert vegetation. 



Finally the striking adaptation seen in the catbriar (Smilax) may be 

 mentioned. The leaf of this plant is provided with two tendrils, which 

 are, erroneously, I believe, usually regarded as of stipular nature. These 

 are situated near the base of the petiole. A transverse separation-layer 

 is formed in this leaf in the petiole above the tendrils, so that, although 

 the blade is shed, the plant is still supported in position by the now 

 woody tendrils, which persist through the winter and are of remarkable 

 strength. 



It will be seen, I think, that this subject offers an attractive field for 

 observation, and is especially suitable for field study for students. 



PURE SCIENCE AND THE "PRACTICAL." 



Admirable work has been done by Dr. George T. Moore, of the U. S. 

 Department of Agriculture, in developing ' ' a method of destroying or 

 preventing the growth of algae and certain pathogenic bacteria in water 

 supplies." t It has been shown that copper sulphate, " in a dilution so 

 great as to be colorless, tasteless and harmless to man, is sufficiently toxic 

 to algae to destroy or prevent their appearance. ' ' It is probable that copper 

 in some form may be used to destroy mosquito larvae. It is evident that 

 the results of Moore and Kellerman will be of very far-reaching economic 

 importance. The Bulletin which embodies the results of their investiga- 

 tions exemplifies in an exceptional way the unexpected practical outcome 

 of investigations in pure science. Few people would have suspected that 



*" The spines of Fouquieria." Bulletin Terr. Club, 31 : 45. January, 1904. 

 + Bur. Plant. Ind., Bull. 64, by George T. Moore and Karl F. Kellerman. 



