THE PI.ANT WORI.D 211 



by individuals belonging to a species which is usually attacked is due to 

 the absence of the special cheraotactic agent from these individuals.* 

 Further, that parasitism in fungi is an acquired habit. 



BUD SCALES AS NECTAR GLANDS. 



The Para Rubber Tree (^Hevea brasiliensis) possesses two kinds of 

 extra-floral nectaries. t These are (l) small circular glands, similar 

 apparently to those seen in the castor-oil plant, which occur on the 

 upper surface of the petiole, near the bases of the leaflets, of which there 

 are three; and (2) large conspicuous glands occurring on certain of the 

 bud scales. These are stipular in nature, and the lowermost of a bud are 

 of the ordinary functional type, that is, are protective in nature. Above 

 these, however, the stipules become thickened, nearly circular in trans- 

 verse section. The epidermis of their upper surfaces is made up of one 

 to three layers of columnar glandular cells, the secretion of which collects 

 beneath the cuticle, by the bursting of which the nectar escapes. This 

 appears to be the only instance recorded of bud scales serving as nectaries. 



ROOTS NOT AEROTROPIC. 



The view has generally been accepted that the roots of ordinary 

 plants are sensitive to gases, or more particularly, that they curve toward 

 or away from oxygen, hydrogen, and carbon -dioxid. Such, however, 

 seems not to be the case. Miss Mary E. Bennett \ has experimented with 

 the tap-roots of corn, pea, radish, cucumber and lupine seeds, and has 

 shown that the curvatures made by these roots, such as had previously 

 been observed by Molesch and attributed to their aerotropism, are due 

 not to their reactions toward gases but toward water. 



The relation of De Vries's theory of mutation to Darwin's theory 

 of the origin of species may be said to be not generally well understood. 

 For this reason every teacher and student will find it profitable to read 

 a very interesting article by a countryman and near neighbor of Professor 

 de Vries, Professor Hubrecht, of the University of Utrecht. It is to be 

 found in the Popzdar Science MontJily for July, 1904. The key-note of 

 the paper lies in the following words, " * * * his (De Vries's) great 

 and imperishable merit consists in this, that his important and extensive 

 experiments have provided us with a reliable basis concerning a subject 

 about which Darwin had not fully made up his mind." 



*Ann. Bol., April, 1904. 



t Parkin, J., Ann. Bot., 18: 217, April, 1904. 



t "Are Roots Aerotropic? " Bot. Gazette, 37 : 241, April, 1904. 



