18 PLANT LIFE 
and nutriment the Chlamydomonas plant 
rapidly multiplies in a vegetative or non- 
sexual manner. This is brought about by 
the division of the protoplasmic contents, 
within the membrane, into a number of 
smaller lumps, each of which becomes a small 
image of the original parent. They are 
commonly two, four, or eight in number, and 
finally escape from the ruptured membrane of 
the “‘ mother cell’ into the surrounding water 
where they grow, and may give rise in their 
turn to new individuals. 
Now such a plant as Chlamydomonas is 
relatively very simple, and yet it already 
exhibits the most striking characters that 
distinguish the majority of plants. 
In the first place its living substance is 
enclosed in a membrane, and in the second 
its protoplasm contains a green chloroplast. 
In order to grow it must clearly obtain food, 
but the presence of a membrane precludes 
it from acquiring any except such as is already 
dissolved in the water. No solid particles 
can pass the membrane and so reach the 
protoplasm, but water and substances dis- 
solved in it will readily do so. The whole 
of the mineral food substances, and such 
gases as oxygen and carbon dioxide, reach 
the protoplasm in this, and only in this way. 
But this external membrane not only 
limits the nature of the food-supply, but as 
the size and complexity of the body increase, 
it continues more and more to restrict the kind 
