42 



ACADEMIC BOTANY. 



LESSON IX. 



PLANT DEVELOPMENT CONTINUED. 



Series II. — Fhanerogamia. 2 Classes 



1. Gt/mnoeperm^f Naked Seeds. 



2. Angioapermse, Covered Seeds. 



Class I. Gymnosperm^. Naked Seeds. 



73. Central Link ; Cycas. 74. Cone-bearers ; Yews. 75. Cypresses. 

 76. Pines. 77. Fertilization. 78. Joint-Firs. 79, 80. Welwitschia. 

 81. Gymnospermous Growth. 



73. The Oymnosperms (Gymnogens) are the central link 



in the chain of Natural Suc- 

 cession or development (see 

 full-page illustration, Lesson 

 I.). They constitute what 

 iVvi are termed Comprehensive 

 ^h Types; including (compre- 

 <'}.A hending) among themselves 

 characters which belong to 

 classes widely separated from 

 one another. The Oycas 

 leaves are circinate in bud, 

 .ill\ing it to the Ferns; the stem is 

 alniost wholly cellular, another Cryp- 

 toiiamous trait; it yields large quanti- 

 tu- of starch which make the Sago 

 commerce. The stem is simple, 

 w 11 h the habit of both Tree-Fern and 

 I'.ilm; the leaves are so palm -like 

 tluit the Cycas is miscalled Sago- 

 I'.ilm (sago being furnished from its 

 piih). The embryo has two coty- 

 ledons; but these are unequal and 

 united for the greater part of their 

 length, with only a slit near the 



Fio. 43. — Ovule - bearing 

 leaf of Oycaa revolvta^ re- 

 duced two -thirds: /, un- 

 changed leaflets; »k, sW, 



oriowe-rSr "'^ """ plumule through which it may es- 



