262 PHYSIOLOGICAL BOTANY. 



transparent and provided with their corpuscles. In the 

 transverse section, they appear to be situated in the centre 

 of the cells, whilst in the longitudinal section they are 

 generally seen to be adherent to the wall. They have a 

 flattened form, hence they are detected with difficulty in 

 this aspect. At this period, the granular matter has for 

 the most part disappeared. In the youngest internodes, 

 which have ceased to elongate, and commonly in the next 

 internode also, nuclei still exist in a few of the cells, but 

 they are usually situated upon the lateral walls of the cells. 

 They disappear in the older internodes. 21. During the 

 earliest period of the growth of the stem, neither the pro- 

 duction of new cells, nor their expansion, nor the thicken- 

 ing of their walls is dependent upon the presence of the 

 terminal bud, or upon the leaves existing at the end of 

 the articulation. 



These excellent investigations might form the basis of 

 the theory of the growth of plants. It is very desirable 

 that similar investigations should be made upon Dicoty- 

 ledons, the sterns of which are subdivided by nodes, and 

 then upon Monocotyledons. The merismatic increase in 

 the number of cells in those plants which the author has 

 examined appears to me proved. There can be no doubt, 

 however, that the septa which are produced must be 

 double ; the manner in which they are formed still re- 

 mains to be determined. In many cases, the growth 

 certainly does not take place according to a geometrical 

 progression ; in these an interstitial growth of cells must 

 occur, perhaps in combination with merismatic division. 



It is completely decided by all the investigations which 

 have been made, that no formation of cells within cells 

 ever occurs either during the growth, in length or thick- 

 ness, of vegetable structures, unless we regard merismatic 

 division as such, which would be incorrect. It is by no 

 means my intention to deny the occurrence of this mode 

 of formation in those cases where perfectly new bodies or 

 parts are formed, and the formation of the young plant in 

 the embryo-sac furnishes an instance of the production of 

 cells within cells. 



