312 



I\IANUAL OF POISONOUS PLANTS 



is brought about. After fertilization, the egg cell divides and gives rise to an 

 ■embryo. The mosses differ from the ferns and their allies in a less difJerentiatioti 

 •of tissues and a slight development of shoot and root system. The vascular 

 system and leafy shoots and roots are marked in the ferns. 



PTERIDOPHYTA 



Spores alike or unlike microspores and megaspores developing into flat or 

 irregular prothallia; these bear the reproductive organs, (antheridia and arche- 

 gonia) ; flowers and seeds absent; usually a well developed vascular system. 



This sub-division includes the class Filicales or ferns proper. The class 

 Bquisetales or horsetails; the Lycopodiales represented by the common club 

 anoss, (Lycopodium). 



Fig. 116b. Fern. A. Section through frond of As- 

 pidium Fvlix mas, a leaf-like body with parenchyma cells, 

 an epidermis and vascular bundles x 100. B-I. Develop- 

 ment of the sporangia of Aspidium irifoliatum x 350. K. 

 Young sporangium of Nephrolepis exaltata in the act of 

 differentiating the annulus x 350. L. Immature sporangium 

 of Blechnum occidentale, seen from the back. M. Sporangi- 

 um with spores. N. Sporangium dehiscence at st, a jointed 

 ring X 120. O. Group of spore mother-cells x 350. P-R. 

 Single spore mother-cells in different stages of partition 

 X 425. S,T. Bilateral tetrads of Aspidium Filix mas. U. 

 Mature spores of Aspidium Filix mas x 500. V. Tetrads 

 After lyuerssen. 



