30 



MANUAL OF BOTANY 



the separating walls are present, so that the filament is divided 

 into a number of chambers, which are not cells but coenooytes. 



This eoenocytio structure may extend into some of the mor- 

 phologically most highly complex bodies. Thus the Alga 

 Caulerpa, which attains considerable size and whose body shows 

 rounded stems and much-divided leaves, is composed of only a 

 single coenocyte, whose cavity extends through all the ramifica- 

 tions of the plant. The Fungus Mucoi- mucedo shows a similar 

 structure {fig. 780). 



In cases where the Thallophyte is composed of masses of 



Fig. 780. 



Fig. 7 



CoEuocyte of Mucor mucedo. 



cells there may be considerable histological differentiation, or 

 there may be but little. In some of the brown seaweeds we find 

 a limiting layer, enclosing a very different internal tissue. 

 In some this is composed of elongated loosely arranged cells 

 with mucilaginous cell walls ; in others it shows differentiation 

 into more complex structures. Thus in Macrocystis we find 

 under the epidermal layer a layer of thin- walled parenchyma 

 covering a layer of somewhat prosenchymatous cells with 

 thickened walls, sometimes with pits upon them. The inner 

 portion of this contains the well-marked sieve tubes already 

 referred to. Some of the large Algae of the same group as 



