434 SUMMARY OF CURRENT RESEARCHES RELATING TO 



point of view of the mode of pollination of the flowers. As compared with 

 Arctic Norway, Greenland is very poor in insects, and the flowers display 

 a corresponding increased tendency to autogamy. This is well illustrated 

 in Menyanthes trifoliata, which, instead of being heterostylous, as elsewhere, 

 has become completely isostylous. 138 species of anemophilous plants are 

 named, exclusive of the willows. The entomophilous flowers of Green- 

 land all possess nectar ; but the number of scented flowers is small. The 

 flowers appear to decrease in size with the increase of latitude ; and 

 the brilliancy of colour certainly does not become greater. There are a 

 considerable number of unisexual entomophilous flowers. The author has 

 made no exact observations on the species of insects visiting the flowers. 



Pollination of Flowers.* — Dr. J. M'Leod has observed that if pollen- 

 grains are thrown into a weak aqueous solution of sugar, they will, in a 

 few hours, all burst or put out their pollen-tubes ; but that if the solution 

 is made more concentrated, the putting out of the pollen-tubes will cease. 

 For each species there is an optimum concentration, and a maximum con- 

 centration, beyond which no emission of iiollen-tubes takes place. In the 

 case of heterostylous flowers (^Primula elatior, Hottonia palustris), he finds 

 the maximum concentration to be lower for the small than for the large 

 pollen-grains. Dr. M'Leod adds a series of observations on the visits to 

 flowers of night-flying moths, and of the mode of insect-pollination of a 

 number of species from different localities. 



Germination of the Cocoa-nut Palm.l — Prof. J. von Sachs describes the 

 development of the seedling cocoa-nut. At the commencement of the ger- 

 mination the young embryo, only a few millimetres in size, is split in two 

 by the growth of the cotyledon, its basal portion, which contains the growing- 

 point of the stem, penetrating into the hard putamen, and putting out the 

 first roots and shoot. At the same time, there is formed at the apical end of 

 the cotyledon a swelling of very loose tissue, the haustorium, which eventually 

 attains the size of a small onion. This organ gradually consumes the 

 whole both of the milk and the endosperm, carrying the nutrient material 

 to the growing seedling, and, at the same time, excreting a ferment. 

 By this time, which occuj)ies about tw^o years in cultivation, but probably a 

 much shorter time in the tropics, four or five leaves have been formed. 



(2) Nutrition and Growth. 



Absorption of Carbonic Anhydride by Leaves.^ — MM. P. P. Deherain 

 and L. Maquenne cite determinations which confirm the conclusions already 

 arrived at by them, namely, that the absorption of carbonic anhydride by 

 vegetable tissues is a true phenomenon of solution varying with the 

 temperatm-e, as in all cases of absorption of gas by an inert solvent ; 

 consequently, w'hen the leaf respires in an atmosphere kept at constant 

 pressure, this gives rise to a sui^ersaturation comparable with that of a mass 

 of water into which calcium carbonate and hydrochloric acid have been 

 introduced simultaneously. This absorption of carbonic anhydride by 

 leaves is extremely rapid, at any rate when the leaves are in a vacuum, in 

 consequence of the large surface exposed. 



Increase in thickness of Palm-stems.§— By examination of the stem of 

 a considerable number of species of palm, the late Prof. A. W. Eichler con- 



* Bot. CentralLl., xxix. (1887) pp. 116-21, 150-4, 1S2-.5, 213-6. 

 t SB. Pbys.-Med. Gcsell. Wiirzburg, 1886, pp. 20-3. 



X Ann. Agronoiu., xii. (188G) pp. 526-34. See Jouru. Chem. See. Lond., 1887, Abstr., 

 p. 172. Cf. this Journal, 1885, p. 678. 



§ SB. K. Preuss. Akad. Wi^s. Berlin, 1886, pp. 501-9 (1 pi.). 



