CHAPTER XVII 

 PTERIDOPHYTES 



We have studied that group of plants and the subdivisions 

 (the seed-bearing phmts) which you may consider the most 

 important and we have learned that there are three other great 

 groups. (Chapter V.) Although these groups furnish us com- 

 paratively little in the way of food, clothing and building ma- 

 terials, yet they are of great interest and of considerable value 

 to man. To the botanist they are esj^ecially interesting because 

 we cannot get a thorough knowledge of the plant kingdom with- 

 out studying them. They are of value to all of us because many 

 plants belonging to these groups are of commercial value. There- 

 fore, let us consider the next highest group, the Pteridophytes, 

 which includes the ferns and the related plants. 



True Ferns. — The largest and most familiar group is the 

 order Filicales or true ferns. (Fig. 97.) These plants have 

 true roots, stems and leaves, but the structure of the stems is 

 quite diiferent from anything we have studied. The stems may 

 be short and erect or creeping, underground type known as 

 rhizomes, giving rise to many roots and to the masses of green 

 foliage with which we are familiar. But in tropical countries 

 we frequently find the beautiful tree ferns with their very large 

 trunks. If we cut a cross-section of a stem and examine it under 

 a compound microscope we find a well-developed fibro-vascular 

 system composed of practically the same tissues as in the higher 

 plants but arranged quite differently. The wood cells are in 

 the centre surrounded by the bast cells which are in turn sur- 

 rounded by an endodermis. This is known as the concentric 

 arrangement. These bundles are weak as compared with bun- 

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