y 
3 
i 
1876.] Botany. 231 
plants or very coarse weeds soon clothed the earth from which the six 
feet of soil had been taken. But among the many plants which came 
up at the northern end of the plaza was a vast quantity of Broteroa 
trinervata, a species which is very restricted in its range near the city. 
The only locality from which the fruits of this plant could have been 
brought by the wind was south of the plaza; but on account of the sur- 
roundings of the city, south and north winds are unknown. It seems 
likely to Professor Ernst that the seeds had remained under the cement 
of the old market-place for more than thirty years, and had been there 
preserved unharmed. When the cement was broken up and the ground 
graded for the plaza, the buried seeds, or rather fruits, were exposed to 
atmospheric influences, to moisture, warmth, and air, and after the lapse 
of so long a time germinated. 
The second case relates to a very common weed, shepherd’s-purse, 
which, strange to say, is so rare at Caracas that it had not been met 
with in botanical excursions covering a period of twelve years. Two 
years ago, in the southern part: of the garden of the monastery a place 
was graded for the erection of a building. A great deal of soil was re- 
moved and a wholly fresh surface was thus uncovered. Upon this spot 
many weeds sprang up, and among them thousands of specimens of 
Capsella bursa-pastoris, or shepherd’s-purse. Professor Ernst concludes 
that in this case, as in the other, the seeds had remained dormant in 
the soil for an unknown period. These cases belong to the same class 
as those mentioned by Hoffmann, and given in the January number of 
the NATURALIST. 
TROPICAL Trees DURING THE Dry SEAson. — Professor Ernst, of 
Caracas, states that many woody plants of the Venezuela flora lose all 
their leaves during the dry season, even when the ground is copiously 
watered for the purpose of preventing their fall. Several large-leaved 
plants, such as Cassia, mahogany, and many others, exhibit this phenom- 
enon. The new foliage starts usually when the rainy season sets in, but 
if the rains come very late, as they did in 1875, many of these trees un- 
fold their buds and develop the leaves at a period when the ground is 
dry and hard, the tropical heat very intense, and the air extraordina- 
nly dry. This curious periodicity has been casually noticed by several 
Writers, but no explanation has been hitherto offered. Professor Ernst 
has given this subject careful study, and now states that in general, those 
trees which cast their foliage in the dry season have compound leaves of 
rather delicate texture: From such leaves transpiration is exceedingly 
rapid, and early carries away all the available water. When there is no 
more moisture within reach of the plant, the leaves separate from the 
stem. In this wholly or partially leafless condition the trees remain 
Until the end of April or the beginning of May, when the moist winds 
from the northwest, as precursors of the tropical rains, awake the slum- 
& vegetation. Of course the trees cannot absorb by their parts 
