ZOOLOaT AND BOTANY, MICROSCOPY, ETC. 269 



The ovules also, though apparently of normal size and form, usually 

 display some degree of functional atrophy. In hybrid Begonias in which 

 the stamens are transformed into staminodes, the ovules are destitute of an 

 embryo-sac. In other cases, even when the number of ovules is reduced 

 below the normal, they still retain their fertility when the pollen-grains 

 have become altogether sterile. 



Hybrid-pollination.* — Prof. E. Strasburger gives the results of a large 

 number of further experiments on the extent to which pollen-grains from 

 one species will germinate on the stigma of another species. His observa- 

 tions and experiments have led him to the conclusion that the pollen- 

 grains contain a diastatic ferment, which can often be readily recognized 

 by its rapid and energetic action on starch-paste. This ferment appears 

 to be of the greatest importance to the nutrition of the pollen-grains as 

 their tubes pass through the tissue of the style. It is probable also that 

 there are other ferments which have the property of attacking cellulose, 

 that it is the action of this ferment which enables the pollen-tube to 

 pierce cell-walls, and that the nature of the ferment must differ in different 

 species. The action is probably the same in the hyph^ of parasitic fungi 

 which penetrate the host. The same explanation may be offered of the 

 penetration of the pollen-tube into the embryo-sac, and of the general 

 capacity for pollen-grains to impregnate only ovules belonging to their 

 own species. 



Vitality of PoUen-grains-t — M. L. Mangin has experimented on this 

 subject with pollen-grains from a number of different species, when 

 germinating both naturally and on specially prepared nutrient solutions. 

 For the latter he finds a convenient preparation to be agar-agar softened 

 and dissolved in boiling water, glucose, saccharose, gum, or dextrin being 

 then added. The period during which the pollen-grains retain their power 

 of germination varies between one day in the case of Oxalis Acetosella, and 

 eighty days with Narcissus pseudo-narcissus and Picea excelsa. As a general 

 rule the germinating period is short for those species which remain in 

 blossom for a long while. The rapidity with which the grains germinate 

 after coming in contact with the nutrient fluid also varies, some putting out 

 their tubes immediately, others not till after the lapse of several days. 

 Light has a favourable effect on the growth of some pollen-grains, an 

 unfavourable effect on others. 



Fertilization of Achlys tripliylla.| — Dr. S. Calloni describes the 

 structure of the flower of this species, a native of western North America, 

 which differs from the typical Berberideaa in being dichogamous and in the 

 absence of a nectary, and apparent absence also of a corolla. In the first 

 two of these points it approaches the Lardizabalege. It is proterandrous 

 and anemophilous. 



Fertilization of Aconitum Lycoctonum.§ — According to Herr C. 

 Aurivillius the flowers of this plant are dimorphic, some having the spur 

 straight, others curved upwards into nearly a semicircle. The plant is 

 strongly proterandrous, and is visited largely by humble-bees, and ap- 

 parently hardly at all by any other insects. Of these some have a proboscis 

 too short to reach the nectary at the base of the spur ; these bite through 



* Pringsheim's Jahrb. f. Wiss. Bot., xvii. (1886) pp. 50-9 (1 fig.). Cf. this Journal, 

 1886, p. 279. 



t Bull. Soc. Bot. France, viii. (1886) pp. 337-42. 



J Arch. Sci. Phys. et Nat., xvi. (1886) pp. 452-9. 



§ SB. Bot. Siillsk. Stockholm, Feb. 17, 1886 (2 figs.). See Bot. Centralbl., xxix. 

 (1887) p. 125. 



