CHAPTER VI 



the Poly podium, with its numerous fibrous roots, strong root-stock, 

 and prominent woody bundles and veins, should be made a text for 

 reviewing the physiology of higher plants, especially the functions of 

 woody tissue. The habits and adaptations of the ferns are perhaps 

 sufficiently emphasized in the Reader. Fern leaves are very cleverly 

 disposed in the bud, the delicate tissue is infolded, and the stronger, 

 woody tissue forms a spherical screen about it ; at the same time the 

 petiole, or its continuation, the mid-rib, is an arch that pries up the 

 soil, then straightens itself and draws out the unfolding leaf. The 

 devices for guarding against both too much and too little evaporation 

 are similar to those possessed by other plants in the same habitats. 

 The reason for the immunity of ferns from the attacks of animals is not 

 so obvious. They are also said to be little troubled by fungi, but the 

 golden-back is sometimes infested with a rust. 



The spore-cases of ferns are remarkably attractive objects under 

 the microscope ; they are very easily mounted and do not require 

 high powers. The Polypodium in February is likely to have spore- 

 cases in all stages of development, those forming the darkest brown 

 spots, being, perhaps, cases that have already thrown their spores. It 

 is not really at all strange that the growth of ferns from the spore should 

 have been unknown until the days of microscopes. The superstitions 

 about fern "seeds" are quite characteristic of the science of the 

 Middle Ages. There was, indeed, one skeptical spirit who proved 

 that one need not go alone nor use magic spells to collect the "seeds,"' 

 but he did not dream of proving by experiment whether or not they 

 were seeds. The arrangement and coverings of the spore-cases, or 

 sporangia, form a basis for the classification of our ferns. As has 

 been noted, some sori, as the collection of sporangia are called, are 

 naked, others are protected by rolled back margins, others by a 

 special membrane called the indusium. 



There is an exquisite little floating plant, the Azolla, sometimes 

 called the.water fern, that is common in still water. Single plants 

 are not more than half an inch long, but in the mass their tints of 

 pale green, purple or almost red, are very attractive. The reproduc- 

 tion of our Azolla has been carefully worked out by Professor Camp- 

 bell, of Stanford University. 



The Equisetum, or horsetail of the picture, is the most common 

 one in California. The fruiting cones are mature in March and 

 April, when the food-making fronds are just beginning to develop. 

 There is another form of Equisetum with a long, unbranched stem , 

 the fruiting cones being borne at the end. As noted in the Reader, 

 the spores of the Equisetum are hygrometric ; when dry they cling 



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