RECENT ADVANCES IN VEGETABLE CYTOLOGY. 27 



attach to each one severally, the existence of such well- 

 defined boundaries is by no means an indispensable condition 

 of great complexity of organisation. Caulerpa amongst the 

 algae imitates very closely the differentiated form of some 

 of the higher terrestrial plants, without however possessing 

 their corresponding internal structure. Its protoplasm is 

 bounded by an external wall only, and is not internally 

 partitioned. And yet the characters distinctive of the 

 energids in the leaf-like parts are assuredly different from 

 those of the energids which exist in the creeping stem or 

 rootlike fibres. A transition from the condition of Caulerpa 

 to that of the higher plants may be seen in Cladophora, in 

 which the filamentous body seems, at first sight, to be made 

 up of chains of cells, each of which stands in a definite 

 relation to the general symmetry of the branched plant ; 

 nevertheless, closer examination shows that each "cell" is 

 multi-nucleate, and really represents a federation of energids 

 which so act together as to constitute morphological units as 

 far as the external form of the plant as a whole is concerned. 

 Sachs' conception of the energid has been assailed by 

 some writers, and he has to some extent perhaps invited 

 criticism by formerly affixing a quasi-morphological, as well 

 as a physiological significance to the term. At first sight 

 it may seem difficult to justify its application in those cases 

 in which streaming movement happens to go on in certain 

 layers of the protoplasm, whilst the layer in which the 

 nuclei are embedded is at rest. It is obvious that if we 

 admit, as we can hardly avoid doing, that the nucleus does 

 really exert a directive action over a localised area, the 

 migratory protoplasm (assuming the movement to affect the 

 protoplasm, and not merely the granular bodies contained 

 in it) must be constantly coming within the range of 

 fresh centres of influence. It may perhaps be compared 

 to the case of a person passing from a region presided 

 over by one government into one under the jurisdic- 

 tion of another. Such a person would naturally be subjected 

 to changed conditions, without however affecting either his 

 own identity or that of the particular political centres through 

 which he may happen to travel. 



