ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 77 



form sometimes assuming a convexo-concave shape. If the original 

 form is maintained, this is eflfected by longitudinal ribs. The number 

 of pores has no systematic value ; the development of spines and 

 other emergences depends on the law of the greatest economy of 

 space. The pores are so arranged that at least one always comes into 

 contact with the stigmatic fluid. When there is only one pore, this 

 is a compensation to the abundant development of pollen as a pro- 

 tection against self-fertilization. 



Fertilization of Philodendron.* — E. Warming describes the 

 phenomena connected with the fertilization of Philodendron bipin- 

 natifidum, belonging to the Aracese. The period of blossoming 

 extends over from 34 to 36 hours ; about 7 p.m. on the first day a 

 great increase in temperature takes place in the staminodes and male 

 flowers, to the extent of 18 • 5° C. excess over that of the surrounding 

 air; no increase of temperature takes place in the female flowers; 

 between 9 and 10 a.m. the next morning a second rise takes place to 

 the extent of from 5° to 7°. About noon of the first day an aromatic 

 odour is perceptible, and towards noon of the second day there is an 

 abundant exudation of an aromatic sap. The anthers open between 

 4 and 5 p.m., and about 7 the blossoming is at an end. The author 

 considers that fertilization is effected by pollen from the same spike, 

 carried by small black bees, not by snails, as has been supposed. 



Fertilization of the Prickly Pear.t — Dr. E. E. Kunze sees in the 

 irritable stamens of Ojpuntia vulgaris, a provision for securing cross 

 fertilization by insect aid. In fair weather each flower opens on two 

 successive days. Hive-bees, flies, and humble-bees were seen to visit 

 the flowers for nectar, in obtaining which they grasp clusters of 

 stamens, which, when released, fly up against the pistil, from which 

 they slowly recede to their former position. Although the legs of 

 the insects were covered with masses of pollen after visiting a flower, 

 they were not seen to creep over the stigmas. The pollen-grains are 

 therefore supposed to be thrown between the stigmas after the sudden 

 movement of the stamens following the retreat of an insect. It is 

 hardly necessary to add, however, that crossing is well effected by the 

 insects in question, the motion of the stamens insuring a thorough 

 dusting of their bodies with pollen. 



Annual Development of Bast.| — C. Hielscher has examined 

 twenty-six different dicotyledonous and coniferous trees with respect 

 to the amount of fresh bast formed each year. He finds that it does 

 not consist of such well-marked regularly recurring zones as the wood 

 in its annual rings. The primary bast always consists of both hard 

 and soft bast ; the secondary bast, formed every year, has usually the 

 same composition, though in some cases, as Alnus and Fagus, after the 

 second year soft bast only is developed. The amount of bast produced 

 annually consists of three or more tangential rows of soft bast-cells. 



* Engler's Bot. Jahrb., iv. (1883) pp. 328-40. See Bot. Centralbl., xv. (1883) 

 p. 372. 



t Bull. Torrey Bot. Club, x. (1883) pp. 79-81. Cf. Science, ii. (1883) p. 381. 

 X Abhandl. Naturf. Gesell. Halle, xvi. pp. 113-39. 



