152 BOTANY 



mination of the pollen grain on the stigmatic surface of the flower, 

 enters the ovule in the pollen tube and unites with the egg cell. 

 This process, known as fertilization, is the most important event 

 in the life of the plant, for it is only by means of this process that 

 the ovule is stimulated to become a seed. The fertilized egg 

 grows into the young plant within the seed, known as the embryo 

 see page 34). 



This method of reproduction, called sexual reproduction, is 

 found in the spermatophytes, that is, all seed-producing plants. 

 In the flowerless plants a somewhat similar process takes place. 

 Seeds are not formed, however, but structures called spores repro- 

 duce the plants. 



Sexual and Asexual Spores. — A spore is usually considered to 



be a cell which has become dormant, but which will under favor- 



• able conditions again germinate to form a new 



plant. A spore, as we shall see, may be formed in 



one of several ways. If formed by the union of 



two cells, as is the fertilized egg, it is then said to 



mold, highly be a sexual spore. If, as is frequently the case, 



magnified. ^j^^ spore is formed by the separation of a bit of 



protoplasm from the plant to form a resting cell, then it is called 



an asexual spore. In most of the so-called " spore plants " both 



sexual and asexual spores are formed at different times during 



the life history of the plant. 



Pteridophytes 



The Ferns and their Allies. — The fern plants include the true 

 ferns, the horsetails or scouring rushes, and the club mosses. The 

 true ferns are moisture-loving and shade -loving plants; they play 

 an important part in the vegetation of the tropical forests. Many 

 forms are found in the temperate regions; we even have some com- 

 mon ferns that remain green all winter. The ferns are among 

 the most beautiful of our plants, and the study of a common form 

 will amply repay the time so spent. 



The Polypody (Polypodium vidgare)} — The habitat of the polypody 

 is damp woods and rocky glens. The ferns are usually hard to get up 



^ Hunter and Valentine's Manual, page 93. 



