98 PRIMITIVE FORMS OF LIFE 



a high degree of complexity. Certain forms attach themselves 

 to submarine rocks by means of processes like the roots of 

 higher plants ; or the body of the plant may elongate into a 

 cylindrical cord resembling a stem with lateral ramifications, 

 sometimes flattened, which might therefore be called leaves. 

 We would be tempted to assume that Algae such as these 

 having become terrestrial, were metamorphosed as a group 

 into plants analogous to those that grow in our fields to-day, 

 were it not that the mechanism of their origin is apparently 

 more complicated. 



Fungi, obviously later in origin than Algae, but dominated in 

 their evolution by the necessity to lead a parasitic life, have not 

 attained such a high degree of complexity. Their most highly 

 developed forms consist of elongated filaments variously inter- 

 twined, and wound in places, which become attached to one 

 another and come up out of the ground, or erect themselves upon 

 the surface of the plants in which they have developed, and 

 finally spread out to form that cap-shaped fructifying organ which 

 we know so well both as a delicious food and a deadly poison. 



The terrestrial plants which form the group of the Mosses, 

 always very modest in size, still bear a close resemblance to the 

 Algae as regards their structure. In the class of Muscineae, to 

 which they belong, we can even trace gradations between a 

 flattened thallus in the form of a continuous lamina found in 

 certain Hepaticae, and the thallus of those Mosses which exhibit 

 a small cylindrical stem bearing leaves laterally. Only the 

 root is absent. 



In the case of the Mosses, however, reproduction has taken 

 a special line which tachygenesis will modify in the higher 

 plants by making it pass through successive stages, each of 

 which will be characteristic of some main branch. The lower 

 Algae generally reproduce themselves by means of corpuscles, 

 which we call zoospores, provided with minute paddles, 

 whip-like threads or waving cilia, enabling them to swim. 

 In these Algae the zoospores are all alike, in others, 

 however (Ulothrix, Tetraspora), they can, according to 

 circumstances, either remain alike in character and give birth 

 singly to new algae, or take on two different forms : one large- 

 sized, which accumulates reserve substances in its protoplasm, 

 the other small, and without these reserves. A large zoospore 

 can then only develop into a new alga if it first unites with a 



