INVEKTEBRATA, CRYPTOGAMIA, MICROSGOPY, ETC. Ill 



Influence of the Hygrometric State of the Air on Vegetation.*— 

 According to M. P. Sagot, leaves transpire but little in an atmosphere 

 charged with aqueous vapour ; the axis, therefore, and the leaves, 

 remaining strongly turgid, develop to an excessive extent, to the 

 detriment of the flowers and the fruit. Moreover, if the amount of 

 soil is but small, the quantity of mineral salts that accumulates in the 

 tissues is often too small for the seeds to ripen. In a dry atmosi^here, 

 on the contrary, the transpiration being very energetic, the turgidity 

 of the tissues is always low, and the growth therefore slow. This 

 state of things is most favourable to the development of the flowers 

 and fruits, as well as to the rij)ening of the seeds, even in poor soils ; 

 for the salts, contained in comparatively concentrated solutions, 

 finally accumulate in considerable quantities in the tissues. 



The reason is thus furnished why, in equatorial forests, the trees, 

 ■which are bare of leaves during the dry season, burst into blossom 

 under the influence of moist winds even before the rain falls, and bulbs 

 begin to grow as soon as the air is moist. The growth of some of 

 our vegetables, especially the cabbage, is often arrested during the 

 drought of summer, even when they are well watered. But as soon as 

 rain falls, however small in amount, transpiration is diminished, and 

 the growth is at once rapidly accelerated, diminishing again afterwards, 

 even if the rain continues ; because the supply of mineral substances, 

 accumulated during the drought, begins to exhaust itself. Vegetables 

 such as haricot, maize, pea, corn, &c., grown in greenhouses, even in 

 the soil, become feeble, in consequence of the too large quantity of 

 aqueous vapour in the atmosphere. This is, however, not the case 

 with all plants; there are some, on the contrary, such as ferns, 

 palms, Scitamincfe, Aroideee, Piperacea3, Melastomacese, &c., which 

 require a moist air. 



The structure of the tissues varies with the degree of moisture of 

 the air. If a shrub is transplanted in summer from a hothouse to 

 tlie open air, it soon loses its leaves, which are replaced by smaller 

 ones, more crowded and of a firmer texture. These fall in their turn 

 when, in the autumn, the tree is replaced in the hothouse. For the 

 same reason the leaves fall from the trees in equatorial forests at the 

 commencement of the rainy and of the dry seasons. 



Plurality of Nuclei in Vegetable Cells.f — This phenomenon, 

 according to M. Treub, has hitherto only been observed, and that as 

 an exception, in the cells of Alga), especially the Siphonocladaceo) ; 

 also in the pollen-grains, pollen-tubes, and cells connected with the 

 embryo-sac. 



He now points out that it is a constant occurrence in the vegetative 

 cells of some ])hanerogams ; thus in the liber-fibres and laticiferous 

 cells of some Enpln^rbiaceaj, Asclepiadcro, AjwcynacciV!, and Urticaccas 

 — cells which Do Bary has proved to be simple and single — a 

 plurality of nuclei occurs with some regularity : for instance, in the 

 liber-cells of Tlnmidns iKjndus, Urtica dioiea, Vinva iitinor, and in the 

 laticiferous colls of the two last named and of Euphorbia, itc. 



♦ ' Bull. Sop. Bot,. Franco,' xxvi. (1870) p. 57 ; «co also unu; p. 100, 

 t '(J(.iiq)tt.s Kcndii.s,' Ixxxix. (1870) ]>. \'.)\. 



