PLANTS WITHOUT SEEDS 
25 
because these tubes carry water to any part of 
the plant that needs it. During the coal-form¬ 
ing ages, many ferns were as tall as trees. In¬ 
deed there are tree-ferns still, but they grow only 
in warm countries, or in green-houses. It is a 
big advantage for a plant to be able to grow tall, 
for then its leaves can get more sunlight. Sun¬ 
light is necessary for the manufacture of food. 
From this advantage comes another one: if a 
plant can manufacture a great deal of food, it 
can store some away for the winter season. 
Then it can stay alive all winter and be ready 
to grow in the spring. The mosses and earlier 
plants never have extra food nor storage places. 
The ferns are a big improvement over them. 
They can stay alive much longer. 
The ferns, like the mosses, produce new 
plants by means of spores. The next plant that 
developed in the history of plants was able to 
have true seeds. 
* 
& 
