THE SPERMATOPHYTES 
455 
grows into the soil to form the tap root and in time the remainder 
of the root system. ‘Thus the seedling sporophyte is formed 
which in time develops into the mature White Pine tree 
Gametophyte § t 
Stage yeti 
‘ 
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\ 
‘ 
\ 
\ 
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' 3 
' tage 
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‘ 
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Ly 
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Rex —O.— O- 6 ‘s 
‘e— —@+g-6 4-0-4. 
Fic. 342.—Diagram of life-cycle of a pine. (From Gager after Schaffner.) 
CLASSIFICATION OF THE (GYMNOSPERMS 
The gymnosperms are grouped into 4 orders, as follows 
Order 1. Cycadales, the Cycads. 
Order 2. Ginkgoales, the Ginkgos. 
Order 3. Coniferales, the Conifers. 
Order 4. Gnetales, the Gnetums and Ephedras. 
ORDER CYCADALES 
The Cycads or fern palms, the most primitive of the seed 
plants, are represented by about 100 species of fern-like plants 
that are believed to have been descended from the Cycadofilices, a 
group of fossil plants which possessed the leaf characters of ferns 
and ovules and seeds like the pines 
Most of them have plant 
bodies consisting of a thick cylindrical stem covered by the bases 
of spirally arranged leaves and bearing upon its summit leathery, 
pinnately-compound leaves and scale leaves. The male and 
female cones are borne on different sporophytes. They are 
represented by. the genera Cycas, Lamia, and Dioon. 
