2 



THE CLASSES OF PLANTS. 



best mark of distinction that has hitherto been found ; for it is universally 

 present in plants, and has enabled Mr. Payen to confirm by chemical 

 evidence the vegetable nature of certain productions till lately regarded as 

 Zoophytes, and therefore as belonging to the Animal Kingdom. (Ann. 

 Sr. Xnt. 2. se.r. xx. G.3.) 



But it has been long ago asserted by Bory de St. Vincent, and others, 

 that there exist in nature organised bodies which are animal at one period of 

 tlnir lives, and vegetable at another ! This, if true, would for ever put an 

 end to the possibility of distinguishing the two kingdoms when they shall 

 each have arrived at their lowest forms. Its truth has, however, been denied. 

 On the contrary, Kiitzing, in his recent magnificent work on Algae, insists 

 that it happens in hrs Ulothrix zonata, (Fig. I.) He asserts that in the cells 

 of that plant there are found minute animalcules, with a red eye-point, and a 



transparent mouth-place ; that they are not 

 in fact, distinguishable from Ehrenberg's 

 Microglena monadina ; these bodies, how- 

 ever, are animals only for a time. At last 

 they grow into vegetable threads, the low- 

 est joint of which still exhibits the red 

 eye-point. This phenomenon, which Kiit- 

 zing assures us he has ascertained beyond 

 all possibility of doubt, puts an end to the 

 question of, whether animals and plants can 

 be distinguished at the limits of their two 

 kingdoms, and sufficiently accounts for the 

 conflicting opinions that naturalists entertain 

 as to the nature of many of the simpler forms 

 of organisation. 



Such being the case, it is not worth attempting to decide, whether the 

 lowest forms of structure, to be presently mentioned, belong to the one 

 Kingdom or the other. It will be sufficient that they have been regarded 

 as plants by many eminent naturalists. 



It is in this microscopical cellular state of existence that the Animal 

 Kingdom ends, and the Vegetable commences. It is from this point that 

 the naturalist who would learn how to classify the Kingdom of Plants must 

 take his departure. He perceives that those species which consist of cells, 

 either independent of each other (Rrotococcus, Uredo), or united into simple 

 threads (Conferva, MbniUa), are succeeded by others in which the threads 

 colled Into nets (Hydrodktyori), or plates (Ulm), or the cells into masses 

 (Laminaria, Agaricus)', peculiar organs make their appearance, and at 

 last, as the complication of structure increases, a leaf and stem unfold as 

 distinctly limited organic parts. 



Those simpler plants which exist without the distinction of leaf and stem, 

 are also destitute of flowers ; they are equally without the breathing-pores 

 SO abundantly formed in the skin of more complex species, and they multiply 

 bj the spontaneous formation in their interior, or upon their surface, of repro- 

 ductive spheroids called spores. Among the many names that Botanists 

 have given such plants, that of Titallogens is here preferred. A thallus is 

 B fusion of root, stem and leaves, into one general mass ; and that is much 

 the nature of these elements of Vegetable structure. 



9 il, , !?, T ,', ,B ' X £{? AT t' aft i r Ku ^ in «— '• A P orti ° n of the plant discharging its vegeto-animal- 



" ' f • ,- • 7 mu f h enl » r 8 ed > » n , d In various states of progress into a thread ; 3. a young thread, 



or plant, throe or four days old, much less magnified. ' s ' 



