AGRICULTURAL BOTANY. 429 



upon the roots of a dozen or more species near which they habitually grow, 

 but the structure of the roots does not indicate complete parasitism. Further 

 investigations will be necessary to determine whether the parasitism described 

 is characteristic of the genus or whether it is exhibited only by the species 

 growing near Tucson, Ariz. 



Following this is an account of experiments on xeno-parasitism, or the 

 enforced nutrition of cuttings of a number of species of plants on different host 

 plants, mostly fleshy cacti. Regenerated cuttings were inserted into the host 

 plants and this relationship maintained for two years or more. The xeno- 

 parasite was found to form roots which penetrated the tissues of the host in 

 some instances, while in other cases absorption took place through the epider- 

 mal tissue of the submerged bases of the inserted slips. The development dis- 

 played by the xeno-para sites was in all instances less than that of similar shoots 

 autophytically nourished. Successful xeno-parasitism was found to be de- 

 pendent upon the superior osmotic activity of the parasitic member of the 

 nutritive'couple, although not all pairs of plants sustaining such inequality were 

 capable of becoming host and dependent, there being other limiting factors of 

 minor importance. The relative acidity of the sap of two plants appeared to be 

 of no importance in the determination of their capacity to form a nutritive 

 couple. Such plants as the giant cactus (Carnegiea gigantea) undergo rapid 

 oxidation on injured surfaces and form wound cork so rapidly as to inhibit 

 parasitism, except by species with extremely high osmotic activity, which suffer 

 depletion of their own water balance very slowly and which take solutions from 

 an enforced host against great resistance. Agaves as xeno-parasites were found 

 to form roots so profusely as to destroy the tissues of the host. Experimental 

 arrangements of xeno-parasites were found most successful when regenerated 

 cuttings were inserted in the bodies of the host in a resting condition, in the 

 colder season, with the concentration of the sap increasing, but before the 

 osmotic activity had reached its maximum. 



Studies on the development of bulbous plants, G. Andr6 (Bui. Soc. Chim. 

 France, -}. ser., 7 (1910), Nos. 16-17, pp. 865-869; 18-19, pp. 927-933).— A de- 

 tailed account of investigations noted elsewhere (B. S. R., 23, p. 229). 



A study of elm-tree seedlings showing Mendelian results, A. Henry 

 (Jour. Linn. Soc. [London], Bat., 39 {1910), No. 272, pp. 290-300, j)ls. 5, figs. 

 2). — ^According to the author, there are two well differentiated species of elm 

 in the British Isles, Ulmus montcma and U. glabra. A number of other forms 

 are known which have been given specific names but which are frequently 

 considered as hybrids. Among them is the Huntingdon elm (U. vegeta). 

 Studies have been made of seedlings of this tree, about 5,300 in all being raised. 

 A number of these were examined in regard to leaf characters, as to whether 

 they were opposite or alternate, and also regarding their size, and the author 

 concludes that this species is an undoubted hybrid, the seedlings segregating 

 in Mendelian ratios. 



Observations on other trees, such as oak, birch, poplar, willow, etc., are 

 given, from which it is claimed that many of the so-called varieties of these 

 trees are hybrids of well-known species. 



Male sterility in potatoes, a dominant Mendelian character; with re- 

 marks on the shape of the pollen in wild and domestic varieties, R. N. 

 Salaman {Jour. Linn. Soc. [London], Bot., 39 {1910), No. 272, vp. 301-312).— 

 While studying heredity of color the author noticed the phenoiL.^non of con- 

 tabescence in potatoes, and he has shown that it is a dominant hereditary 

 character. 



A considerable number of varieties of wild and cultivated potaioes were 

 studied in relation to this phenomenon as well as to the character of the 



