10 



in even small glass jars. As a lulo, liowover, tliey grow 

 very slowly and remain sterile, the conditions heing pro- 

 bably very imfavourable. 



b. axatomy axd histology of the 



Vegetative Organs. 



1. — Anatomy of the Shoot. 



The young upright shoot of Chondrus crispus shows a 

 differentiation into several tissues, which are, however, not 

 very easy to separate at the points where they pass into 

 one another (see PI. II.) 



The centre is occupied by very much elongated and 

 comparatively narrow cells (fig-T). These central cells 

 lead to a tissue further out of shorter and stouter cells, 

 from which arise the regular rows of external cells, easily 

 distinguished by their red contents. There is no morpho- 

 logical differentiation of these tissues such as we get in 

 the bodj' of a higher, vascular plant — the differentiation 

 here being of a purely physiological nature. The external 

 cells, distinguished by their dark red colouring form the 

 " assimilating system," the large stout ones next inside 

 form the system of " collecting cells," the central cells 

 form the " conducting tissue." The whole arrangement is 

 based on the assimilation, collection and conduction of 

 food. The assimilating cells have been called the cortical 

 layer, the two other tissues the outer and inner medulla 

 respectively. We will employ the nomenclature based on 

 the physiological function of the respective tissues, 

 although the other terms, cortex, inner and outer medulla, 

 are equally good. 



The tissues just mentioned are seen at their best and in 

 their most characteristic condition a short distance behind 



