154 



LECTURE IX. 



A similar internal differentiation results, however, even in the case where 

 a plant from the subdivision of the Cceloblastge only consists of a single 

 vesicle, the growth and branching of which is not accompanied by cell divisions at 

 all. Among the Coeloblastag in this connection are especially to be mentioned the 

 marine Algce Codium and Halymeda. These are plants of considerable size, variously 

 segmented, and apparently composed of masses of tissue ; a transverse or longitudinal 

 section, slightly magnified, presents apparently an ordinary plant tissue, resembling 

 that of many other Algae, until closer inspection shows that the apparent cell tissue 

 consists of the ramifications of a tubular cell in itself continuous, the thousand-fold 

 repeated outgrowths of which are more or less segmented by constrictions. Here 

 also the comparison of Fig. 164 will show the true state of the case. One has only 

 to observe that Fig. B represents the longitudinal section of A^ perpendicular to the 

 plane of the paper, and indeed only through a small portion of the length of one 

 of the Opuntia-like segments of the shoot. It is perceived at once, that the vesicles 

 form at the periphery of the shoot a dense layer, representing to a certain extent an 

 epidermis; and that in the axis the vesicles run longitudinally and are long-jointed, 

 representing a looser vesicular system traversed by interstices, between the epidermal 

 tissue and the axial strand, which however, corresponding to the form of the shoot, 

 is to be imagined broad and flat. 



