64 PLANT-LIFE 



We shall conclude this chapter with a reference to 

 an order of Alga? whose affinities are obscure. The 

 Siphoned to which we refer, are marked off from other 

 Alga? by the nature of their thallus, which, in spite of 

 often being much branched, is tubular, and not com- 

 posed of cells enclosed within their several cell- walls. 

 The tube is a product of a single cell, and its membrane 

 encloses a continuous protoplasmic body, containing 

 many chloroplasts and nuclei. Compartments, formed 

 by transverse septa, occur in the more complex forms. 

 Many species, such as those belonging to the genus 

 Caulerpa, are marine. The species of this genus are 

 much varied in form; they occur in tropical and sub- 

 tropical seas, often growing in great masses or beds. 

 No matter how varied the forms are, or how branched 

 they may be, the thallus always consists of an uninter- 

 rupted tube. These marine plants might be accused of 

 mimicking such land plants as Cactuses, Ferns, Horse- 

 tails, Mosses, etc. Multiplication seems to be due to 

 parts of the thallus breaking away and developing into 

 new plants; no sexual cells have as yet been observed 

 in any forms. 



Botrydium granulatum, another member of the 

 Siphonese, exhibits great capacity of adaptation to 

 changes of conditions. This little plant occurs on the 

 moist margins of ditches and ponds, especially on 

 loamy soil. It has a green, balloon-like shoot, never 

 more than about J inch in diameter, which appears 

 above ground, and a colourless, branched, rootlike 

 portion that grows into the soil. It is a one-cell plant, 

 whose cell-membrane encloses a continuous cavity, 

 which is not only evident in the upper part, but is also 



