Dear Sir,

Many thanks for your highly encouraging letters.¹ The first I did not answer hitherto, because I expected to find an opportunity to visit once more our plains, where I intended to pay a close attention to the point of your inquiry.² However this opportunity is not yet come: my professional work at the University keeps me month after month in town, and when holidays come, there are examinations, and special commissions, and I do not know what not. When I first saw the plains (in February 1874), it was at the end of the dry season; and though there are undoubtedly a good many plants with glaucous leaves (especially Cyperaceæ and Eriocaulaceæ),³ I do not recollect that the general appearance of the flora struck me as glaucous. I think it would be best to make observations in the middle of the rainy season, where any difference ought to be more striking.

I am very glad that my observation on Melochia was of any interest for you, and shall attend to your indications in further experiment.⁴ I think heterostyled flowers are far more numerous than is generally believed. I lately noticed that Turnera ulmifolia is in the same case, though there is scarcely any difference in the shape and size of the pollen grains.⁵ I am preparing to make a series of experiments with this species, and shall later report on them.

There is in this Turnera another point, which I think is sufficiently interesting to be studied carefully; unfortunately I am not able to do it. The two glands at the base of the leaves are very remarkable organs. Morphologically I believe them to be either modified teeth of the margin, or atrophied lateral leaflets. A vascular bundle enters each of them. The produce a sugary secretion, which appears on their surface as a clear drop, where it is eagerly sucked by ants. It is next to impossible to find one single plant without half a dozen or more of these insects fairly stationed among the rather densely crowded leaves on the upper end of the stems. Besides this secretion of sugar, there are a great many sphaeraphides of oxalate of lime in the tissue of the gland. This circumstance appears to me of interest, and suggestive of the question whether there can be a certain relation between both substances. But this point I must leave to persons more versed in organic chemistry than I am. I may be allowed to add, that I never saw an ant, nor indeed, any other insect, in the corollas of Turnera.⁶

Just when I was examining the glands of Turnera, I received Bonnier’s memoir “On Nectaries”, publ. in the Annales de Sciences naturelles. I must confess that I cannot agree with his conclusion that the physiological work of any kind of nectary is “en relation directe avec la vie de la plante.⁷ If the nectaries produce always substances directly useful for the plant, how is it, I ask, that generally so much, if not the whole of these substances flows away, being thus exposed, as really happens, to be stolen by insects? Every physiological work has of course a certain purpose, but this may be either direct or indirect, and if the first is neither apparent nor demonstrable, it is but natural to look for the second.

I have made observations on two plants, where the direct usefulness of similar productions appears to me out of any question. We have a species of Marcgravia, it is probably the M. acuminata Miq.⁸ The flowers (about 30) occupy an inch more or less of the branch, whilst the 6 to 8 pitcher-like bracts grow all from the very end of the branch. These pitchers are somewhat of the shape of a Phrygian cap, and about two inches long, their peduncle included (see the sketch). They hang of course perpendicular, whilst the flowers are so placed that nearly all of them are in the same horizontal plane. Now, there is honey in the pitchers up to the day when the floral envelops drop off, and fragments of them are still adhering. But as soon as these too are falling away, fecundation must be realized, the stamens wither very soon, and the pitchers are honey-less, dry up, and get black, but remain for some time hanging on the branch. Their honey-making function ends therefore with the opening of the flowers and the probably immediate fecundation of the same, so that there remains nothing for further reabsorption.

Another case is that of Passiflora biflora.⁹ There is in the middle of each leaflobe, on its underface, a conspicuous gland, which produces a considerable quantity of sweet honey. The secretion is so energic, that plants which had been one night kept in my vasculum, had on all their leaves drops of this substance. It is sought after by hymenopterous insects, as I had several times occasion to see. Of what direct use can this secretion be to the plant? The leaves certainly would grow without, nor is the secretion as such useful for the plant, because it must lose by it a large quantity of sugar. It is on the contrary very easy to observe, how the insects in their search for the drops of honey, scramble over flowers on every part of the little creeper, and assist thus in fecundating the stigmata. I have planted some specimens in my little garden, and will try to find out whether there is any fecundation without insects, and whether the plants will grow, when the places of the leaves with the glands are punched out.

Is it known that the fierce little ants, which inhabit the hollow stems and branches of Triplaris americana, keep scale-insects in their lodgings?¹⁰ They are very abundant, and even in the thinnest branches it is easy to discover them among the brown felt-like substance which covers the inside of the wood.

Abutilon striatum Dicks. introduced here from Perú, as people say, thrives not any longer, and never set fruit.¹¹ I have seen humming-birds attacking the flowers from outside, perforating the calyx, and thus robbing the honey. I have been told that about 40 years ago, Señor Antonio L. Guzman, father of our actual President,¹² brought one plant from Peru, and that from this by cuttings all the other specimens were derived. In the last years all have small leaves with many yellow spots, and flower very poorly. The species is evidently dying out with us.

Some years ago a friend of mine discovered in the mountains towards the south of Caracas the very handsome Ionidium anomalum HBK (Nov. Gen. et Sp. V, pl. 500), and brought seeds, which were sown in several gardens. The plants grew everywhere, but none produced ripe seeds. It is evident that insect help was wanted, as might have been expected, the large snow white labellum of the flower looking just like a beautiful landing-place for welcome visitors.¹³ I have lately obtained good seeds by artificial fecundation, but only from two flowers.—

I apologize for this long letter, but hope that you will excuse me, as I am desirous to communicate to you some facts which perhaps are not entirely void of interest. Unfortunately this year I am bound to teach mineralogy, a study which is somewhat out of my line, so that it keeps up nearly all my time. We have here the queer old system of a Professorship of Natural History, so that I must lecture one year on botany, one year on Zoology, and another year on Mineralogy: rather hard work in our times! And this the more so, as with respect to Geology, there is no poorer place on God’s earth than the valley of Carácas, entirely built of metamorphic rocks, and showing nothing else but interesting examples of gigantic denudation. Field-work, with me the best thing I use to do with my students, is therefore not very productive. In this connection I take the liberty to make you a request. I have nearly every line you have published, but not your works on Coral Reefs and on the volcanic islands and parts of South America.¹⁴ Would you honour me with a copy of each of them? It is needless to say that I would prize both as tokens of your kindness towards an humble, but sincere, fellow-worker in the extensive fields of your scientific researches.

Allow me to add that Venezuela belongs now to the postal Union, so that simple lettres pay no more postage than 2$\frac{1}{2}$ pence, and printed matter a halfpenny for every 50 grammes.¹⁵ I think you had a shilling stamp on your last letter.

I am, dear Sir, very truly yours | A Ernst