522 Minnesota Plant Life. 



egg is not ejected and remains in the organ where it was 

 formed, awaiting fecundation. Certain brown seaweeds ilhis- 

 trate the first condition. The sperms and eggs are ejected into 

 the sea water, where they find each other and pair. The sec- 

 ond condition is that of the red seaweeds and of the whole 

 series from mosses to seed-plants. Moreover, it essentially 

 characterizes the fungi and many of the bright-green algae. 

 In the management of their eggs plants remind one somewhat 

 of the mammals. Because of the small size and concealment 

 of plant eggs they are not familiar objects like those of insects, 

 fishes and birds. 



On account of their motile character, sperms are much more 

 likely to be lost than eggs, consequently plants produce them 

 in much greater numbers. Ordinarily many thousand sperms 

 are constructed for one egg that is fecundated. But in 

 seed-plants where the male grows as a parasite upon tissues 

 close to the location of the female, only a pair of spermatozoids 

 are needed, one for each egg produced by the female. In such 

 forms the cells that are peculiarly in danger are the pollen- 

 spores and these are commonly formed in extraordinary pro- 

 fusion. 



Fecundation. The fusing of sperm and egg is known as 

 fecundation. After fusion the egg is said to be fecundated. 

 Exactly the meaning of the process is not clear. It is known 

 that by it the offspring derives the benefit of a double Hne of 

 inheritance, thus enabling it to make favorable variations, and 

 perhaps accommodating it more precisely to its surroundings. 

 But a single sperm fuses with each egg, and after this has taken 

 place the egg commonly secretes a membrane which before was 

 absent, and thus shuts out later sperms that might attempt 

 a fusion. The cell mechanics of the fecundation process are 

 decidedly complex, for this is by no means a mere blending of 

 two masses of living substance, but is an orderly reorganization 

 of the two structures into one. Not every portion of the egg 

 is fitted to receive the sperm. There is generally a particular- 

 spot on the egg surface at which the fusion takes place. This 

 is known as the "receptive spot," and in some forms it differs 

 in color and texture from the rest of the egg. The swinmiing 

 lashes of the sperm seem always to blend with that portion of 



