46 OUTLINES Of PLANT LIFE. 



EXERCISE XII. 



A leafy liverwort (Porella flaiyphylla). 



1. In what position do the plants grow with reference to the sub- 

 stratum ? 



Disentangle carefully a single plant.* Observe 



2. The growing apex ; the dying base ; the distinctly dorsiventral 

 habit. Enumerate the differences between the upper and under sides. 



(H 54.) 



3. The mode of branching : a central axis, with lateral branches, 

 themselves with lateral branches ; i.e., monopodial and bipinnate. (^ 58.) 



4. The yellowish or brownish stem, covered with leaves unequally 

 distributed. 



5. The two rows of large leaves on the upper flanks of the stem. 

 How do they overlap ? Turn the shoot over and note a third row of 

 small underleaves in the center below ; also right and left the lobes of 

 the upper leaves. Determine the form of the under and upper leaves. 

 Make an enlarged paper pattern of the latter showing how their ventral 

 lobes are arranged. (Figs. 40, 41.) 



6. Demonstration. Mount a leaf and point out the uniformity of cells 

 and their abundant chloroplasts. 



Mosses. 



In the mosses the complexity of the mature vegetative body 

 is somewhsit greater. It is always developed as a shoot dif- 

 ferentiated into stem and leaves. 



55. Rhizoids. — The shoot is anchored, as in the liver- 

 worts, by numerous usually much branched rhizoids {A, fig. 

 42 ; w, fig. 43). Similar filaments may be produced, often 

 in great numbers, along the stem and especially inthe axils 

 of the leaves, or they may even arise from the leaves them- 

 selves, when the plants grow in dense patches or in a very 

 moist place. 



56. The stem is usually cylindrical and covered by the 

 crowded leaves. In structure it generally shows an advance 

 upon that of the liverworts, which is nearly uniform, in hav- 



* If dry, first soften by placing plants in hot water for a few minutes. 



