184 ELEMENTS OF STRUCTURAL BOTANY. 



CHAPTER XXI. 



EXAMINATION OF A FERN A HORSETAIL A CLUB-MOSS. 



324. We shall now proceed to the examination of some 

 common plants which will be found to be typical of groups 

 differing in important respects from the phanerogams. 



Ferns. Fig. 231 is a representation of our com- 

 mon Polypody. You may find it in almost any shaded 

 rocky place. Running horizontally beneath the surface 

 you will find the stem of the plant, which in this case is, 

 therefore, a rhizome. A portion of the rhizome is shown 

 in the lower part of the figure, with fibrous roots on the 

 under side. From the upper side are developed the 

 leaves, which, as you see, have long petioles, and if you 

 find one which is still in the bud you will observe that it 

 is rolled up lengthwise, as shown in Fig. 232. The 

 vernation is, therefore, circinate, and this is the case in 

 nearly all the Ferns. On examining the back of the leaf 

 (Fig. 231 shows the back) we observe rows of brownish 

 dots on each side of the middle veins of the upper lobes. 

 Fig, 233 is an enlarged view showing the position of these 

 dots at the extremities of the veinlets. When we put one 

 of these dots under the microscope it is seen to be a 

 cluster of minute, stalked bodies, such as that shown in 

 Fig. 234. These bodies are further found to be sacs filled 

 with extremely fine dust, and the dust consists of multi- 

 tudes of rounded particles all exactly alike. They are, in 

 short, spores, and the sacs m wnich they are contained 

 are the spore-cases, or sporangia ; while the clusters of 

 sporangia are the fruit-dots, or sori. Around each spor- 

 angium there is an elastic jointed ring which breaks at 



