April 2, 1885. ] 
JOURNAL OF HORTICULTURE AND COTTAGE GARDENER 
275 
Beech. This determines the width, and by compelling the leaf to 
lengthen itself leads to the peculiar form which it assumed. Moreover, 
not only do the leaves on a single twig admirably fit one another, but 
they are also adapted to the ramification of the twigs, and thus avail 
themselves of the light and air, as we could see by the shade they cast 
without large interspaces or much overlapping. In the Sycamores, 
Maples, and Horse Chestnuts the arrangement is altogether different. 
The shoots are stiff and upright, with leaves placed at right angles to the 
plane of the branch, instead of being parallel to it. The leaves are in 
pairs and decussate with one another, while the lower one3 had long 
petioles which brings them almost to the level of the upper pairs, the 
whole thus forming a beautiful dome. For leaves arranged, as in the 
Beech, the gentle swell at the base is admirably suited, but in a crown 
of leaves, such as those of the Sycamore, space would be thereby wasted, 
and it is better that they should expand at once, as saon as their stalks 
had carried them free from the upper and inner leaves. Hence we see 
how beautifully the whole form of these leaves is adapted to the mode of 
growth and arrangement of the buds in the plants themselves. 
In the Black Poplar the arrangement of the leaves is again quite 
different. The leafstalk is flattened, so that the leaves hang vertically. 
It would be observed that, while in most leaves the upper and under 
surfaces are quite unlike, in the Black Poplar, on the contrary, they are 
very similar. The stomata, or breathing-holes, moreover, which in the 
leaves of most trees are confined to the under surface, are in this species 
nearly equally numerous on both. The Compass Plant of the American 
prairies, a yellow Composite, not unlike a small Sunflower, is another 
plant with upright leaves, which growing in the wide open prairies 
tends to point north and south, thus exposing both surfaces equally to 
the light and heat. It was shown by diagrams that this position also 
affected the internal structure of the leaf. 
In the Yew the leaves are inserted close to one another, and are long 
and linear, while in the Box they are further apart and broader. In the 
Scotch Fir the leaves are linear, and 1J inch long ; while in other Pines, 
the Weymouth for instance, the stem is thicker and the leaves longer. 
In the plants hitherto mentioned one main consideration appeared to be 
securing as much light as possible ; but in tropical countries the sun was 
often too powerful, and the leaves, far from courting, avoid the light. 
The typical Acacias had pinnate leaves, but in most Australian species the 
true leaves are replaced by a vertically flattened leafstalk. It would be 
found, however, that the seedlings have leaves of the form typical in the 
genus. Gradually, however, the leaf becomes smaller and smaller, until 
nothing is left but the flattened leafstalk or phyllode. In one species the 
plant throughout life produced both leaves and phyllodes, which gave it a 
very curious and interesting appearance. In Eucalyptus, again, the young 
plant has horizontal leaves, which in older ones are replaced by scimetar- 
shaped phyllodes. Hence the different appearance of the young and old 
trees which must have struck every visitor to Algiers or the Riviera. So 
much for deciduous trees. 
In evergreens the conditions are in many respects different. It is 
generally said that leaves dropped off in the autumn because they died. 
This, however, is not strictly correct. The fall of the leaf is a vital 
process, connected with a change in the cellular tissue at the base of the 
leafstalk. If the leaves were killed too soon they do not fall. The 
lecturer illustrated this by some twigs which he had purposely broken in 
the summer ; below the fracture the leaves had been thrown off, above 
they still adhered, and so tightly that they could support a considerable 
weight. In evergreen trees the conditions were in many respects very 
different. It is generally supposed that the leaves last one complete year. 
Many of them, however, attained a much greater age ; in the Scotch Fir 
three or four years; in the Spruce or Silver six or seven ; in the Yew even 
longer. It followed from this that they require a tougher and more 
leathery texture. When we had an early fall of snow our deciduous trees 
are often much broken down ; glossy leaves had a tendency to throw it off 
and thus escape ; hence evergreen leaves were very generally smooth and 
glossy. Again, evergreen leaves often have special protection, either in 
an astringent or aromatic taste, which rendered them more or less 
inedible, or by thorns and spines. Of this the Holly is a familiar 
illustration, and it was pointed out that in old plants, above the range of 
browsing quadrupeds, the leaves tend to lose their spines and become 
unarmed. The hairs on leaves are another protection. On herbs the 
presence of hairs is often associated with that of honey, as they protect 
the plants from the visits of creeping insects. Hence, perhaps, the 
tendency of water species to become glabrous, Polygonum amphibium 
being a very interesting case, since it is hairy when growing on land, and 
smooth when in water. 
The lecturer then dealt with cases in which one species might be said 
to mimic another, and he exhibited a striking photograph of a group of 
Stinging Nettles and Dead Nettles, which were so much alike as to be 
hardly distinguishable. No one could doubt that the Stinging Nettle was 
protected by its poisonous hairs, and it was equally clear that the in¬ 
nocuous Dead Nettle must profit by its similarity to its dangerous neigh¬ 
bour. Other similar cases were cited. Reference was next made to 
aquatic plants, many of which bad two kinds of leaves, one more or less 
rounded, which float on the surface, and others are cut up into narrow 
filaments, which remain below. The latter thus present a greater extent 
of surface. In air, however, such leaves would be unable to support even 
their own weight, much less to resist any force such as that of the wind. 
But in perfectly still air, for the same reason, finely divided leaves might 
be an advantage, while in comparatively exposed situations more compact 
leaves might be more suitable. It was pointed out that finely cut leaves 
are common among P w herbs, and that some families which among the 
low and herb-like species had such leaves, in shrubby or ligneous ones 
had leaves more or less like those of the Laurel or Beech. 
An interesting part of the subject is connected with the light thrown 
by the leaves of seedlings. Thus the Furze has at first trifoliate leaves, 
which gradually pass into spines. This showed that the Furze was 
descended from ancestors which had trifoliate leaves, as so many of its 
congeners had now. Similarly, in some species, which, when mature, 
have palmate leaves, those of the seedling were heart-shaped. Perhaps 
in all cases the palmate form is derived from the heart-shaped, and when 
in any genus we found heart-shaped and lobed leaves, the former might 
represent the earlier or ancestral condition. If there is some definite 
form told off for each species, then surely a similar rule ought to hold 
good for each genus. The species of a genus might well differ more 
from one another than the varieties of any particular species ; the generic 
type might be, so to say, less closely limited ; but still there ought to be 
some type characteristic of the genus. One genus is that of Senecio (the 
Groundsel). In addition to Senecios more or less resembling the common 
Groundsel, there were species with leaves like the Daisy, bushy species 
with leaves like the Privet and the Box, small trees with leaves like the 
Laurel and the Poplar, climbing species like the Tamus and Bryony. In 
fact, the list was a very long one, and showed that there was no definite 
type of leaf, but that the form in the various species depended on the 
condition of the species. From these and other considerations the lec¬ 
turer concluded that the forms of leaves do not depend on any inherent 
tendency, but to the structure and organisation, the habits and require¬ 
ments of the plant. Of course it might be that the present form had 
reference to former, and not to present conditions. This rendered the 
problem all the more complex and difficult. The subject presents a very 
wide and interesting field of study, for if he were correct in his con¬ 
tention, every one of the almost infinite form of leaves must have some 
cause and explanation. The lecture, illustrated by numerous diagrams 
and specimens, was listened to with considerable interest. — (The 
Standard.) 
FIXING RAIN GAUGES. 
ONE of the first essentials in meteorology is uniformity; in fact, it 
might be described as not only one of the first, but as the first, for without 
Fig. 50. 
it comparisons are impossible. Hence chiefly it is that I find myself 
reluctantly obliged to protest against the somewhat tempting arrange¬ 
ment of rain gauge and thermometer stand drawn by Mr. Inglis in your 
issue for March 12th (page 219). 
Experiment has shown that every foot that a rain gauge is raised 
above the ground causes it to collect less rain ; we require to know the 
amount which reaches the ground, and therefore gauges are placed as near 
thereto as is practicable. At one time their orifices were often only 2 or 
3 inches above the ground, but it wa3 proved that gauges so placed collected 
too much, because rain and hail splashed in from the surrounding ground. 
Hence the height of 1 foot was adopted, an 1 at the present time there are 
at least 1700 rain gauges in this country so fixed. I leave it to your 
readers to judge whether overwhelmingly strong reasons must not be 
produced before it can be advisable to break up such a splendid approach 
to uniformity. 
There are other minor matters in Mr. Inglis’s sketches to which I am 
obliged to take exception. The funnel, for instance, is too shallow to 
hold more than an inch or so of snow; all good gauges are now provided 
with what are known as Snowdon funnels (see sketch)— i.e., with a short 
cylinder—which enables them to retain any moderate amount of snow. 
Again, the joint where the funnel passes through the lid c in fig. 39, just 
above the letter D, is sure to prove a source of trouble ; a few seasons of 
sun, wet, and frost will make it leaky, and though in the engraving there 
is the representation of what is known as an umbrella— i.e , an arrange¬ 
ment for throwing such leakage outside the bfftle—I know that in prac- 
