20O THE TEACHING BOTANIST 



(Muehlenbeckia), or extremely elongated (climbers), and 

 others with compound leaves of different kinds, some lacking 

 petioles and stipules, and others showing the leading systems of 

 phyllotaxy well, with some to show how this is disregarded in 

 the final arrangement of the leaf blades. Some showing the 

 leaf function assumed by the stem may be added, including the 

 extreme case in the common " smilax " of the greenhouses. 

 In such work as this, the use of a good scientific greenhouse 

 is particularly advantageous. Valuable plants for this purpose, 

 found in such houses, are Ruscus hypoglossum, Colletia, Utex, 

 Acacia, the latter showing the phyllodes, often with compound 

 lower leaves. 



Several students may work upon one plant, and they are 

 to be exchanged occasionally. Red labels may be placed 

 upon those to be studied in a greenhouse. 



Pedagogics. - - This exercise is for training in morphology ; 

 also to give an idea of different modes of venation and com- 

 pounding of leaves, and the main systems of phyllotaxy ; but 

 especially it is to make plain how great may be the changes 

 in size and shape of parts while they retain their original 

 nature, a subject of the utmost importance, and at the very 

 foundation of morphology. The students thus trace out how 

 the leaves alter shape, become compound, have or have not 

 petiole and stipules ; how the stem lengthens or shortens ; 

 how buds multiply or are suppressed, etc., while the relative 

 positions of the parts remain unchanged. Every part may be 

 a centre of variation in form and size. A good conception to 

 place before the students in the summary of their studies is 

 this : to imagine each part indefinitely elastic and compressible, 

 so that any of them may be either greatly drawn out or re- 

 duced, while the relationship of position of stem, leaf, and 

 axillary bud remains unchanged. 



