I have had the house full of visitors, and when I talk I can do absolutely nothing else; and since then I have been poorly enough, otherwise I should have answered your letter long before this, for I enjoy extremely discussing such points as those in your last note. But what a villain you are to heap gratuitous insults on my ELASTIC theory: you might as well call the virtue of a lady elastic, as the virtue of a theory accommodating in its favours. Whatever you may say, I feel that my theory does give me some advantages in discussing these points. But to business: I keep my notes in such a way, viz., in bulk, that I cannot possibly lay my hand on any reference; nor as far as the vegetable kingdom is concerned do I distinctly remember having read any discussion on general highness or lowness, excepting Schleiden (I fancy) on Compositae being highest. Ad. de Jussieu (36/1. "Monographie de la Famille des Malpighiacees," by Adrien de Jussieu, "Arch. du Museum." Volume III., page 1, 1843.), in "Arch. du Museum," Tome 3, discusses the value of characters of degraded flowers in the Malpighiaceae, but I doubt whether this at all concerns you. Mirbel somewhere has discussed some such question. Plants lie under an enormous disadvantage in respect to such discussions in not passing through larval stages. I do not know whether you can distinguish a plant low from non-development from one low from degradation, which theoretically, at least, are very distinct. I must agree with Forbes that a mollusc may be higher than one articulate animal and lower than another; if one was asked which was highest as a whole, the Molluscan or Articulate Kingdom, I should look to and compare the highest in each, and not compare their archetypes (supposing them to be known, which they are not.) But there are, in my opinion, more difficult cases than any we have alluded to, viz., that of fish--but my ideas are not clear enough, and I do not suppose you would care to hear what I obscurely think on this subject. As far as my elastic theory goes, all I care about is that very ancient organisms (when different from existing) should tend to resemble the larval or embryological stages of the existing. I am glad to hear what you say about parallelism: I am an utter disbeliever of any parallelism more than mere accident. It is very strange, but I think Forbes is often rather fanciful; his "Polarity" (36/2. See Letter 41, Note.) makes me sick--it is like "magnetism" turning a table. If I can think of any one likely to take your "Illustrations" (36/3. "Illustrations of Himalayan Plants from Drawings made by J.F. Cathcart." Folio, 1855.), I will send the advertisement. If you want to make up some definite number so as to go to press, I will put my name down with PLEASURE (and I hope and believe that you will trust me in saying so), though I should not in the course of nature subscribe to any horticultural work:--act for me. LETTER 37. TO J.D. HOOKER. Down, [May] 29th, 1854.