ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
355 
increase in length, subject to a periodicity. With only a few exceptions 
in the trees observed, the growth in thickness exhibited two maxima and 
minima in each season ; but in the different examples, these maxima and 
minima occurred at very different periods of the year. No necessary 
connection could however be established between the period of this 
growth in thickness and the period of the development of the leaves in 
each particular species, although the period of the commencement of 
the formation of the wood coincides with that of the unfolding of the 
leaves. 
Development of Potato-tubers.* — M. A. Prunet refers to the well- 
known fact that the buds towards the summit of the tubers of the potato 
(anterior portion) develope more rapidly than those near the base 
(posterior portion). He finds the anterior portion of the tuber to be 
richer, as a general rule, in dry substance, in carbohydrates, in nitro- 
genous substances, in organic acids, and in salts, in particular, in 
potassa, magnesia, and phosphoric acid. Furthermore, he finds — in 
opposition to the view of Wortmann^ — that the transformation of nutri- 
tive substances is effected, not by the direct action of the protoplasm, 
but by a diastase. At an early period the nutritive substances are 
equally distributed throughout the whole of the tuber ; and it is only 
when it has attained its full size that a transport takes place in the 
interior of the tissue towards the buds in the anterior portion. 
Stem-pressure.}: — Dr. J. Bohm states that he finds every year in 
stems (of the horse-chestnut) a very high positive pressure, sometimes 
amounting to nine atmospheres ; while in the autumn there is a negative 
pressure, which usually attains its minimum in August or September. 
The great positive pressure appears to be due to osmose. The osmotic 
substances are the soluble constituents of the secretion formed during 
the production of the duramen. 
Transmissibility of Pressure in Plants. § — M. G. Bonnier states 
that pressure is transmitted rapidly across the conducting tissues of 
woody plants. In herbaceous plants this does not take place im- 
mediately, and the transmission of pressure is much more feeble than 
in woody plants. In succulent plants the transmission is very slow. 
Ascent of Sap.fl — Prof. S. Schwendener sums up the results of 
recent observations on this subject, and criticizes unfavourably the 
conclusions of Strasburger and Wieler on several points. In opposition 
to their view he contends that the ascent takes place in the older 
annual rings as well as in the peripheral portion of the alburnum, and 
that the libriform tissue may, in certain circumstances, play an important 
part in the phenomenon. He maintains that the bordered pits afford a 
large filtration surface for the sap to pass through. The phenomena of 
the conduction of sap cannot, in his view, be explained without the 
* Comptes Rendus, cxv. (1892) pp. 751-2 ; and Rev. Gen. de Bot. (Bonnier), v. 
(1893) pp. 49-64. f Cf. this Journal, 1891, p. 221. 
X Ber. Deutsch. Bot. Gesell., x. (1892) pp. 539-44. 
§ Comptes Rendus, cxv. (1892) pp. 1097-1100 ; and Rev. Gen. de Bot. (Bonnier), 
v. (1893) pp. 12-28, 74-83, 100-13 (2 pis. and 10 figs.). 
|| SB. K. Akad. Wiss. Berlin, xliv. (1892) pp. 911-46 (1 fig.). Cf. this Journal. 
1892, p. 811. 
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