300 DR. M. J. SCHLEIDEN ON PHYTOGENESIS. 



We must therefore discriminate here three processes essen- 

 tially distinct from each other, which accui'ately considered 

 scarcely find their analogue in the other kingdoms of nature. 



1. The plant grows, i. e. it fonns the number of cells it is to 

 have. 



2. The plant unfolds itself by the expansion and development 

 of the cells that are formed. — It is this phaenomenon especially, 

 altogether peculiar to plants, which, because it results from 

 their composition of cells, can never in any form, not even a re- 

 mote one, occur in crystals or in animals. 



3. The walls of the full-grown cells are thickened by fresh- 

 deposited layers ; — a process which, according to the old rule, a 

 ■potiorifit denominatio,ma.jhe most properly termed the lignifi- 

 cation of the plant. 



If, with regard to the growth of the plant, we keep at present 

 to the meaning of the word given under No. 1 , then this ques- 

 tion will arise — Where are the new cells formed? Three cases 

 here comprise all possible answers : namely, the new cells are 

 either foi-med outside on the surface of the entire previous mass j 

 or in its interior ; and then again either in the intercellular pass- 

 ages or in the cells themselves ; quartum non tlatur. 



Mirbel has,in two excellent and profound memoirs on theilfiar- 

 chantia polymorpha, which he presented to the French Academy 

 in 1831 and 1832 (p. 32), proposed the idea, that all the three 

 cases just mentioned as possible do actually occui* in plants. 

 Without meaning here to anticipate what follows, I must yet 

 remark, that only one case (the formation of new cells in old 

 ones) appears to be proved by his dh'ect observations. The se- 

 cond case is merely a conclusion assumed ; and lastly, the germi- 

 nation of the spores of the Marchantiee, which was to explain 

 the third case, has been observed by me to be quite different, 

 as 1 have already represented above. 



Lastly, however, we must still examine whether the differ- 

 ence of organs establishes a physiological difference of growth 

 which deserves our attention. We may distinguish here four 

 cases. We observe: 1. The development of the plant upwards 

 -{in puncto vegetationis, C. Fr. Wolff). 2. The elongation 

 downwards. We thus comprise the formation of the neces- 

 sary organs of the plant, of the stem, of the leaves, with their 

 metamorphoses, and of the root. 3. We have to keep in view 

 the production of the accidental organs, e. g. bulbs, &c. And 4. 



