220 SUMMARY OF CURRENT RESEARCHES RELATING TO 



induced upon the stem of Lycium halimifolium in a moist place, and 

 the roots removed therefrom, a shoot may arise from the root-stump so 

 formed. If hud-shoots be initiated on the " primary " leaves of Begonia 

 ■carolinieefoHa, which are undivided, several undivided leaves are first 

 produced by these shcots before a divided one appears ; but in the case 

 of one of the shoots induced upon the ordinary digitately divided 

 leaves, a divided leaf is developed at an early stage. It is suggested 

 that the principle of this difference depends upon available food- 

 material. Shoots induced upon an internode without growing-point 

 appear usually arbitrarily, in no fixed order, and only exceptionally are 

 they produced in regular (polar) succession. With root-shoots the 

 reverse is usually the case. Internodes were partially isolated from axes 

 of B. discolor by two cuts made in opposite directions. As a result, 

 roots appeared on the side of the internode left connected with the 

 apical part of the axis and shoots on the opposite side — i.e., the side 

 left connected with the basal or root portion. At the same time roots 

 appeared on that part of the axis above the internode, and shoots on the 

 lower part. Shoots so induced upon the root portion bear, in the 

 autumn, an internodal tuber. This is abnormal, for such are borne 

 normally only upon underground parts, although shoot-tubers may 

 appear in the leaf-axils. Shoots produced similarly by wounding upon 

 Gesnera graciosa revealed no polarity in the order of their appearance. 

 A notable fact was the development of tracheids in the wound-callus, 

 which replaced the severed normal water channels. The number of 

 leaf " regenerates " in Gesneracere was found to depend on the degree 

 of nutrition in the parent plant. Shoots of plants which have already 

 begun to form subterranean tubers may be caused to bear subaerial 

 tubers at the stem-apex and in the leaf-axils. The continued removal 

 of leaf -bulbils acts as a stimulus both to the production of fresh bulbils 

 and to the duration of the life of the leaf. 



General. 



Crataegus : Some Theories concerning the Origin of its Species.* 

 H. B. Brown points out that former systematists conceived of species 

 as being much more composite than they are at present regarded ; the 

 Linnean conception prevailed. Recent workers who have been studying 

 species closely, especially students using the culture method, find that 

 many systematic species are made up of a number of distinct forms, or 

 elementary species that breed true when propagated by seed. The 

 author is inclined to think that a great many of the Cratsegns. forms 

 are hybrids. European species are known to hybridize, and species in 

 several other genera of the rose family hybridize freely. 



Within the past few decades, since the primitive forests have been 

 cleared away, there has been an immense increase in the number of 

 Crataegus plants growing. Being low trees or shrubs, they cannot thrive 

 in dense forests, but spread freely over open pastures and along fence 

 rows. The increase in number of plants makes cross-pollination easier 

 and more probable. Irregularity in the number of stamens and pistils, 



* Bull. Torrey Bot. Club, xxxvii. (1910) pp. 251-50. 



