;■)() 



MIAUTE STRUCTLllK. 



ON THE MINUTE STRUCTURE OF PLANTS. 



The Cell— Tissues— Tissue-Systems- 



genous Stems. 



-Exogenous and Endo- 



Qp to this point we have been engaged in observing such 

 particulars of structure in plants as are manifest to the naked 

 ej'e. We shall now enquire a little more closely, and find out 

 wluit we can about the elementary structure of the different 

 organs. We have all observed how tender and delicate is a 

 little plantlet of any kind just sprouting from the seed ; but as 

 time elapses, and the plant developes and acquires strength, its 

 substance will, as we know, assume a texture varying with the 

 nature of the plant, either becoming hard and firm and woody, 

 if it is to be a tree or a shrub, or continuing to be soft and com- 

 pressible as long as it lives, if it is to be an herb. Then, as a 

 rule, the leaves of plants are of quite a different consistency 

 from the stems, and the ribs and veins and petioles of foliage- 

 leaves are of a firmer texture than the remaining part of them. 

 In all plants, also, the newest portions, both of stem and root, 

 are extremely soft compared wnth the older parts. It will be 

 our object now to ascertain, as far as we can, the reason of svich 

 differences as these ; and to accomplish this we shall have to 

 call in the aid of a microscope of much higher power than that 

 which has hitherto served our purpose. 



The Cell. 



First let us examme under our microscope a very thin slice of 

 the pith of the Elder. You see at once that the whole 

 slice is made up of more or less rounded, nearly trans- 

 i;)arent bodies, rather loosely thrown together, as shown 

 in Fig. 250. Next let us examine, in the same way, a tliin 

 slice of the tuber of the Potato. Here, again, it is evi- 

 dent that the object under examination is wholly composed 

 of enclosed spaces, not so much rounded, however, as 

 those of the Elder pith, because they are more closelj" 

 packed together. Fig. 251 is a representation of two of 

 these spaces. Now look at the leaf of a Moss, and you 

 see again that we have an aggregation of enclosed spaces 

 as before (Fig. 252). So, also, if we examine a hair from 

 the surface of a Petunia or a Geranium, we have some 

 such appearance presented to us as that shown in Figs. 253 

 and 254, the hairs manifestly consisting of several enclosed 

 spaces placed end to end. In short, the microscope 

 reveals to us the fact that every part of a i)lant is made 

 up of such enclosed spaces, varying greatly in shape and 

 size and general aspect, it is true, but alwaj-s (except in 

 some of the very lowest plants) clearly exhibiting boun- 



Fig. 2.oO. 



f:"-. l'5i. 



Fig. 252. 



