Dear Sir

Some month’s have passed since I sent you my last letter. But I did not dare to lay claim to your time devoted as it is to the promotion of science without offering to you something new or at least deserving your attention. During the winter I was obliged to delay the researches about Drosera, about which I made you communications last year; the specimens I cultivated in my study, remained indeed in hibernating state, but did not yield full grown leafes till spring time.¹ In the mean while I engaged a scholar of mine who prepared an inaugural dissertation for Doctor’s examination after the fashion of our German universities, to bestow his studies upon the anatomy of Dionaea Muscipula.²

You will concede that a most scrupulous examination of the whole anatomical constitution of carnivorous plants is wanted to serve as a standard for comparison with the other vegetables. The researches of Dr. Fraustadt forward many interesting peculiarites of the anatomy of Dionaea,³ f. i. the presence of chlorophylle and amylon in the epidermis, the lack of starch in the superior parts of the leaf after feeding with nitrogenous substance, the curious evolution of the leaf e.c.; very curious indeed is also the fact that the leaf of Dionaea shows a double irritability: 1) by mechanical irritation of the sensitive filaments which affects momentarily but only the tissues along the mid rib; 2) by chemical irritation contracting the whole tissues of the lobes but very slowly. A leaf may by contracted by chemical impulses without being sensible against mechanical irritation of the filaments.

The principal value of the memoir which Dr Fraustadt has now completed in my phytophysiological laboratory, consists in his very accurate and elegant drawings which I shall be glad to send you in short time⁴

Dr. Fraustadt excluded from his memoir a morphological and anatomical comparison between Dionaea and the other Droseraceae;⁵ but we are collecting materials for such parallels which will afford I hope the most interesting points of view; For such an undertaking the complete anatomical dissection of all species is wanted; but it is not easy to procure living specimens; perhaps we may get the rarer species from England?

In some weeks I shall send you an essay about your book which I did pen for the “German Review” (Deutsche Rundschau).⁶

Believe me Dear Sir very faithfully | Yours | Ferdinand Cohn