22 PRELIMINARY STUDIES. 



upper side, there is an exchange of gases by osmosis. 

 Oxygen, which is given off by the plants as a waste prod- 

 uct, passes out ; carbon dioxide from the air, which is a 

 food for the plant, passes in. More than one half of the 

 solid matter of plants is carbon derived from this source. 



19. Tear off bits of the epidermis from the upper and 

 under surfaces of the leaf of the White Water Lily 

 (Nymphcea odorata) and the Yellow Water Lily (Nuphar 

 advena) and examine for stomata. Draw. On which 

 side of the leaf are they the more abundant? Make 

 such explanation as you can of what you find. 



20. Examine stomata obtained from around the edges 

 of the leaf of the Nasturtium (TropcBolum majus). A 

 peculiar form of stoma is illustrated by this observation, 

 the water stoma. Such stomata occur in a comparatively 

 small number of plants. They take their name from the 

 fact that they excrete water in drops. 



21. Using material similar to that mentioned in Num- 

 ber 13, observe the buds growing in the axils of the 

 leaves, i.e., just above the point of attachment of the 

 petiole with the stem. Some of these buds will develop 

 into leafy branches, some simply into leaves, some into 

 flowers, and many will not develop at all. 



Sometimes several buds grow in the axil of the same 

 leaf. These are called accessory or supernumerary buds. 

 Examine branches of Red Maple or Walnut for such buds. 



Adventitious buds are those that form at other places 

 than at the ends of branches or in the axils of leaves. 

 The Willow is perhaps the best plant on which to study 

 them. Twigs from Willow hedges or trees that have 

 been kept cut back are sure to show them. 



Terminal buds are those that form at the ends of 

 branches. 



22. Consider the structure of flowers. The Star 

 Flower (Trientalis Americana)^ May Apple (Podophyllum 



