Minnesota Plant Life. 129 



tion. On the contrary, it develops into an entirely different 

 creature, in the body of which there may be produced some 

 thousands of spore-cells and each one of these if planted under 

 favorable conditions, may originate a new first-stage moss or 

 liverwort ])lant. Upon one of the first-stages a great number 

 of buds might then arise initiating the second-stage of the sex- 

 ual form. Thus it is seen that while animals can generalh 

 derive but a single individual from a fecundated egg, mosses 

 and liverworts — and higher plants still more strikingly — are 

 able to bring into existence thousands of organisms from one 

 egg- The only thing analogous to this in animals is the phe- 

 nomenon of true or identical twinning. \\'hen twins are of 

 precisely the same appearance and sex it is believed that they 

 have developed by the two halves of the embryo in its youngest 

 stage separating from each other. Each half, relieved from the 

 pressure of the other, develops now respectively not into the 

 right or left half of the body, as it normally would, but into a 

 separate individual. If one can imagine, not twins nor quad- 

 ruplets, but great numbers, even thousands of individuals to 

 arise from a single animal's Qgg, he would have something com- 

 parable with the condition in plants which is known as alterna- 

 tion of generations. 



The origin of the higher plants. In the light of what has 

 been said it is apparent that the two alternating generations in 

 the life-history of a moss or liverwort are not equivalent to each 

 other, and one of them, the spore-producing generation, has 

 no analogue in the life-history of those animals with which peo- 

 ple are familiar, ^^d^en, in the algae, an egg after fecundation, 

 instead of developing at once into a new organism as an animal 

 egg does, cuts itself in two into a pair of spores, it has accom- 

 plished normally what happens accidentally in the case of true 

 twins. It seems that what is an accident among animals be- 

 came the rule in the plant world; so in other algae the number 

 of spores thus developed from a fecundated egg w^as increased 

 to four or even to eight in the sphere-alga. Then in a little alga, 

 the disc-alga, which has been regarded as standing closest to 

 liverworts, the number of spores was increased to sixteen ; and 

 for one fecundated egg, by this division into sixteen spores, the 

 plant was able, perhaps, to secure sixteen new individuals, pro- 

 10 



