ORBE, June 10, 1827.
. . .Last week I made a very pleasant excursion. You will remember that I have often spoken to you of Pastor Mellet at Vallorbe, who is much interested in the study of the six-legged insects. He invited me to go to Vallorbe with him for some days, and I passed a week there, spending my time most agreeably. We went daily on a search after insects; the booty was especially rich in beetles and butterflies. . .I examined also M. Mellet's own most excellent collection of beetles and butterflies very carefully. He has many beautiful things, but almost exclusively Swiss or French, with a few from Brazil,—in all about 3,000 species. He gave me several, and promises more in the autumn. . .He knows his beetles thoroughly, and observes their habits, haunts, and changes (as far as he can) admirably well. It is a pity though that while his knowledge of species is so accurate, he knows nothing of distribution, classification, or general relations. I tried to convince him that he ought to collect snails, slugs, and other objects of natural history, in the hope that he might gain thereby a wider insight. But he would not listen to it; he said he had enough to do with his Vermine.
My brother writes me that my box has arrived in Neuchatel. As I am going there soon I will take it then. I rejoice in the thought of being in Neuchatel, partly on account of my brother, Arnold (Guyot), and other friends, and partly that I may study the fishes of our Swiss lakes. The species Cyprinus and Corregonus with their allies, including Salmo, are, as you know, especially difficult. I will preserve some small specimens in alcohol, and, if possible, dissect one of each, in order to satisfy myself as to their identity or specific variety. As the same kinds have received different names in different lakes, and since even differences of age have led to distinct designations, I will note all this down carefully. When I have made it clear to myself, I will send you a catalogue of the kinds we possess, specifying at the same time the lakes in which they occur. As I am on the chapter of fishes, I will ask you:
1. What are the gill arches? 2. What the gill blades? 3. What is the bladder in fishes? 4. What is the cloaca in the egg-laying animals? 5. What signify the many fins of fishes? 6. What is the sac which surrounds the eggs in Bombinator obstetricans?
. . .Tell Dr. Leuckart I have already put aside for him the
Corregonus umbla (if such it be), but can get no Silurus glanis.
I suppose you continue to come together now and then in the evening . . .Make me a sharer in your new discoveries. Have you finished your essay on the physiology of plants, and what do you make of it?. . .
BRAUN TO AGASSIZ.
CARLSRUHE, Whitsuntide, Monday, 1827.
. . .I am in Carlsruhe, and as the package has not gone yet, I add a note. I have been analyzing and comparing all sorts of plants in our garden to-day, and I wish you had been with me. On my last sheet I send some nuts for you to pick, some wholly, some half, others not at all, cracked. Schimper is lost in the great impenetrable world of suns, with their planets, moons, and comets; he soars even into the region of the double stars, the milky way, and the nebulae.
On a loose sheet come the "nuts to pick." It contains a long list of mooted questions, a few of which are given here to show the exchange of thought between Agassiz and his friend, the one propounding zoological, the other botanical, puzzles. Although most of the problems were solved long ago, it is not uninteresting to follow these young minds in their search after the laws of structure and growth, dimly perceived at first, but becoming gradually clearer as they go on. The very first questions hint at the law of Phyllotaxis, then wholly unknown, though now it makes a part of the most elementary instruction in botany.* (* Botany owes to Alexander Braun and Karl Schimper the discovery of this law, by which leaves, however crowded, are so arranged around the stem as to divide the space with mathematical precision, thus giving to each leaf its fair share of room for growth.)