542 PHYSIOLOGY. 



Thalamus. The anatomy of the thalamus or receptacle cor- 

 responds with that of the stem. Hollow receptacles, like those of 

 the Rose or of the Apple, in which the carpels are enclosed or 

 imbedded, have essentially a stem-structure, their cambium-layer 

 being placed between the fibro-vascular zone and the outer epi- 

 dermis. 



Anatomical and organogenetic investigations show that inferior ovaries 

 (p. 130) are really cases of adhesion of the imbedded carpels to the 

 expanded upper extremity of the thalamus. 



The parts of the flower, and especially the carpels, show many minor 

 variations of structure not clearly referable to either the leaf or the stem 

 type of structure ; and from these, as well as from numerous exceptional 

 and transitional cases, it must be assumed that the distinction between 

 leaf and axis is not absolute but arbitrary, though it must for convenience' 

 sake be retained. 



CHAPTER II. 



PHYSIOLOGY OF VEGETATION. 

 Sect. 1. GENERAL CONSIDERATIONS. 



Plant Organization. The organization of plants is regulated by 

 a series of laws which exhibit different degrees of generality. 



The most general law of all is that under which protoplasmic substance 

 assimilates inorganic or, more rarely, organic matter, and produces the 

 closed cellular sacs called vegetable cells. This affects all vegetable 

 structure whatsoever. Animal protoplasm has apparently no power of 

 assimilating inorganic matter. 



The Fungi and parasites live on organic matter ; and this is probably 

 the case to a great extent with cultivated plants grown with excess of 

 organic manures. This will be referred to hereafter. 



One degree less general are the laws regulating the forms of the cellular 

 sacs or cells. These determine at the same time the specific form of the 

 plant in the Unicellular Algae. 



Next follow the laws of development of the secondary deposits upon 

 the walls of the cells, which are valid throughout the whole Vegetable 

 Kingdom, but more and more complex in the successively higher classes. 



The laws of combination of the cells into tissues are a little less general, 

 the diversity increasing here again in proportion to the higher position of 

 the species. 



The laws regulating the forms of organs are of very great importance 

 and interest j and in these we have to distinguish two aspects, or, it may 

 be s.aid, two coexistent series. 



