CHAPTER V 

 CY CAD ALES— Continued 



THE LIFE-HISTORY 



Studies of the life-histories of extinct plants are necessarily incom- 

 plete because the preservation is never perfect, and delicate parts, 

 like the gametophytes, the young embryos, and the meristcms, have 

 usually decayed before fossilization began. Consequently, the parts 

 best known are the mature vascular structures and the harder parts 

 of sporangia and seeds. 



In the living cycads, life-history studies are handicapped only by 

 the difficulty in getting material. There are stages in the life-history 

 when collections should be made almost every day ; for other stages, 

 once a week is often enough; and for more than half of the year, once 

 a month is sufficient. Since the material is tropical or subtropical, 

 and trained histologists in those localities are scarce, the difficulty is 

 not in the existence of material, but in securing a well-fixed series of 

 stages. Of course, one can fix his own material, but financial con- 

 siderations prevent botanists from staying a year in a cycad locality. 

 However, cycads are easy to transport, and large cones may be in 

 fine condition three weeks after being taken from the plant. 



THE SPOROPHYTE — VEGETATIVE 



The vegetative features of the life-history will be considered under 

 the topics, "stem," "leaf," and "root." 



The stem. — The cycads have sometimes been described as plants 

 with branched leaves and unbranchcd stems. All have branched 

 leaves, but there is considerable branching in the stem. 



The typical habit is an unbranched stem with a crown of leaves at 

 the top, so that the plant looks like a small palm or tree-fern (fig. 66; 

 see also fig. 54). All of the arborescent forms are called palms by the 

 natives. Dioon is the Palma de Dolores; Microcycas is Palma Corcha; 

 Encephalartos is the Bread Palm; etc. Even in localities where tree- 

 ferns are familiar objects, the natives do not call them ferns. 



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