STUDIES OF SEED-PLANTS 



215 



which is not also found among angiosperms. In the seeds 

 of conifers there may be more than two cotyledons (from two 

 to twelve) ; but botanists do not attach any special signifi- 

 cance to the mere number, since in other respects conifer and 

 dicotyledonous embryos are very similar. 



It is then in the reproductive organs that there is the most 

 striking difference between gymnosperms and angiosperms; 

 and hence the two groups are compared in this connection 

 with the lesson on the reproductive organs (flowers) of the 

 highest plants. 



211. Cones as Reproductive Organs. The pine or other 

 common cone-bearing tree may be taken as a type of the 

 reproduction found in gymnosperms. In addition to the 

 foliage leaves, certain leaves are 

 set apart for purposes of repro- 

 duction. These leaves (called 

 sporophylls, or spore-leaves) are 

 arranged in the form of cones, of 

 which there are two kinds. 



One kind of cone ("male") is 

 small (Fig. 68, A), and each spore- 

 leaf, corresponding to a stamen of 

 flowers, bears on its lower surface 

 spore-cases or pollen-sacs, which 

 produce pollen-grains. Such a 

 cone is often called staminate, 

 the term commonly applied to flowers which have only 

 stamens. 



The other kind of cone (" female ") has a similar structure, 

 but is larger. It is the well-known cone often seen on cone- 

 bearing trees (Fig. 68, B). Each spore-leaf of the larger cones 

 has on its upper surface spore-cases or ovules (two in pine) ; 

 and such a spore-leaf is equivalent to a carpel, with its ovules, 

 in true flowers of angiosperms. In true flowers the carpel 

 folds and grows together to form a pistil with an ovary 



FIG. 68. Diagrams showing 

 structure of cones in section. 

 A, male cone; B, female cone. 

 s, sporophylls or spore-leaves ; 

 o, ovules ; p, pollen-sacs ; e, 

 (black) central endosperm part 

 of ovule. (From Parker.) 



