PARENCHYMA: ASSIMILATING TISSUE. 



[49 



present close beneath the epidermis ; and the same is the case in the green shoot-axes 

 of Equisehim, and still more evidently in the species of Cactus, the huge shoot-axes of 

 which possess a thin green lamella only at the circumference. However, this is not 

 the place to enter more closely into detail respecting the important physiological pro- 

 perties of the assimilating parenchyma, since this can be done in a proper manner 

 only in connection with the theory of the nutrition of plants to be expounded later. 



In what has been said concerning the epidermis, the vascular bundles, and the 

 fundamental tissue, we have a description, superficial though it be, of the typical 

 histological structure of vascular plants, i.e. the Phanerogams and Cryptogams. 

 According to the requirements of the mode of life, the most various deviations from 

 the forms of tissue mentioned 

 may occur; of these we do 

 not propose to treat further, 

 since what has been stated suf- 

 fices as a basis for further phy- 

 siological considerations. As 

 in the treatment of the external 

 segmentation of plants, I shall, 

 in connection with the three 

 typical systems of tissue, again 

 allude to the corresponding 

 differentiations of tissue in the 

 simply organised plants; where 

 we find, according to the nomen- 

 clature introduced earlier, the 

 rudimentary beginnings of the 

 three systems of tissues. If it 

 were here proposed to exhaust 

 all the various histological re- 

 lations of the lower plants, the 

 material for several volumes 

 would present itself; it suffices 



however for my purpose to confine ourselves to a few short remarks, simply to 

 serve for the guidance of the reader. 



It is already known from the first lectures, that in the Mosses, Algse, and Fungi, 

 many organs which in the vascular plants consist of multicellular masses of tissue, 

 are constructed only of single cells, jointed filaments, or simple cell-layers. In such 

 cases, it is obvious that a differentiation into epidermis, fundamental tissue, 

 and vascular bundles cannot be spoken of. Where, however, the organs of 

 the lower plants consist of several or numerous layers of tissue, we always 

 meet with a more or less evident differentiation, which then presents itself as 

 a rudimentary form of the three systems of tissue adopted by us. This is 

 to be seen particularly clearly in the true Mosses, which are nevertheless highly 

 organised. The spore-forming capsule (the sporogonium or moss-fruit) shows, 

 especially in the highly developed typical Mosses, a sharply diff"eienliated epider- 

 mis, which may even be provided with stomata, marked off" from an inner mass 



(550). A in the 

 cellular spaces ( 



ansverse section through the leaf of Sclaginella ittaeqiiati/olia 

 iddle ; B at the margin ; ch chlorophyll grains— the small dots in 

 rains ; eu epidermis of lower side ; eo that of upper side ; / inter- 

 ntaining air ; sp < 



