ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
641 
in the sequel) is relatively shortened. This first period of the germi- 
native phenomena is even all the more shortened if the revivification 
takes place on a young plant which has been dried up in a more 
advanced stage of development. 
Vitality of Annual Plants.* — Referring to the observations on this 
subject by Prof. T. Holm, Mr. T. Meehan advances the view that any 
annual may be made perennial by persistently destroying the flower- 
buds as they appear. Few plants except those which are distinctly 
woody have perennial parts ; in tubers, rhizomes, bulbs, &c., the older 
portions die after new portions have been formed. The power to 
produce offshoots or stolons is the only real difference between annual 
and perennial herbaceous plants. Even in the case of those annuals 
which throw up only a single flower-scape, if the flower-buds are 
removed before they expand, and the flower-stem cut up into sections, 
plants may be raised which will live for many years if annually treated 
in the same way. 
(3) Irritability. 
Hygrochasy.f — Herr P. Ascherson proposes the term hygrochastic 
for those plants in which the bursting of the fruit and the dissemination 
of the seeds (or spores) are brought about by movements resulting from 
the absorption of water by the fruit or collection of fruits ; xerochastic 
for those in which the same results are attained by corresponding move- 
ments resulting from desiccation. The latter is by far the more 
common phenomenon ; but hygrochastic movements are known in 
Awstatica hierochuntica and in some Composite (rose of Jericho), in 
Selaginella lepidophylla , and in the fruits of many species of Mesembry- 
anthemum ; in the capsules of ZygopJiyllum and Fagonia ; in the calyx 
of some species of Prunella and Salvia ; in the mature inflorescence of 
Jberis umbellata , &c. The two following striking instances are now 
recorded : — 
In Lepidium spinosum (Cruciferae) the ripe fruits are when dry 
closely adpressed to the rachis of the raceme ; access of water causes 
the fruit-stalk to bend at an angle of about 45°, and the fruit to burst 
open on slight contact. The bending of the fruit-stalk is occasioned by 
the presence of a “ dynamic tissue ” capable of strong swelling on its 
inner side ; the bursting of the capsule by a peculiar structure of the 
replum. In Ammi Visnaga (Umbelliferse) the phenomena are precisely 
opposite to those in the allied Daucus Carota. When dry the rays of 
the umbel are closely curved together, but expand when moist. The 
cause of this movement is a strongly extensible cushion situated at the 
apex of the axis of the umbel between the points of departure of the 
secondary rays. 
(4) Chemical Chang-es (including- Respiration and Fermentation). 
Function of Salts of Calcium and Magnesium.^ — Herr O. Loew 
has investigated experimentally the function of these two classes of 
salts in the vital economy, and finds an essential difference between them. 
* Proc. Acad. Nat. Sci. Philadelphia, 1892, pp. 160-2. Cf. this Journal, ante , 
p. 67. t Ber. Deutsch. Bot. Gesell., x. (1892) pp. 91-114 (2 pis.). 
% Flora, lxxv. (1892) pp. 368-94. 
1892. 2 x 
