520 



BOTANY 



PART II 



In certain species some of the aerial haulms always remain sterile, branching 

 profusely, while others which produce the terminal ones either do not branch at 

 all, or only at a later stage, and then sparingly. This distinction between the 

 sterile and fertile haulms is most marked in Equisetum arvense and Equisetum 

 Telmateja, in both of which the fertile shoots are entirely unbranched and 

 terminate in a single cone (Fig. 486). ' Resembling in their mode of life a parasite 

 upon the rhizome, they are otherwise distinguished from the vegetative haulms by 

 their lack of chlorophyll and their light yellow colour. 



Equisetum giganteum, growing in South America, is the tallest species of the 



FIG. 487. Equisetum pratense. I, Female prothallium from the under surface, showing the arche- 

 gonia (A). II, Male prothallium with antheridia (A) ; d, cover cells of antheridia. (/ x 17, 

 J/X12. After GOEBEL.) Ill, Equisetum arvense. Spermatozoid : fc, nucleus ; bl, cilia-forming 

 blepharoplast with cilia ; zyt, cytoplasm, (x circa 1250. After SHARP.) IV, Equisetum arvense. 

 Embryo : 1, 2, octant walls. The stem (si) and first leaf- whorl (b) arise from the upper half, and 

 the root (w) and foot from the lower half, (x 165. After SADEBECK.) 



genus ; its branched haulms, supported by neighbouring plants, attain a height of 

 over twelve metres, and are about two cm. in diameter. 



The spores are all of one kind, and on germination give rise to thalloid 

 PROTHALLIA which are generally dioecious (Fig. 487). The female prothallia are 

 larger than the male, and, branching profusely, are prolonged into erect ruffled 

 lobes at whose base the archegonia are produced. In structure the archegonia 

 resemble those of the Ferns, but the upper cells of the four longitudinal rows of 

 cells constituting the neck are more elongated and, on opening, curve strongly 

 outwards. The spermatozoids, like those of ferns, bear numerous cilia. The first 

 leaves of the embryo are arranged in a whorl and encircle the apex of the stem. 

 The growth of the embryo is effected by the division of a three-sided apical cell 

 (Figs. 487 IV, 100, 101). 



