364 



BOTANY. 



E. sylvaticum, E. limosum, and some other species. In 

 other species, as E. hyemale, E. Icevigatum, the aerial steins 

 also persist; the latter are hence known as perennial- 

 stemmed. 



475. — Tte prothallia are irregularly branched thallns-like 

 growths, composed of chlorophyll-bearing parenchymatous 

 cells arranged in one or more layers. Upon the under side 

 they bear root-hairs, which fix them to the ground. They 

 are usually small in size, ranging from two or three to ten or 

 twelve mm. in length. In most species the prothallia are 

 dioecious, bearing but one kind of 

 sexual organ upon each, and in such 

 cases it always happens that those 

 which bear the antheridia are much 

 smaller than those which bear arche- 

 gonia. Both kinds live but for a 

 short time, the whole period of their 

 existence usually not extending be- 

 yond a few months ; the male pro- 

 thallia appear to endure for a some- 

 what shorter period than those which 

 bear archegonia. 



476. — The antheridia occur upon 

 the ends or margins of the prothal- 

 lia ; they arise from the repeated 

 division of a marginal cell, thus 

 forming an inner mass of cells rich 

 in protoplasm, and a coTering layer 

 {an', Fig. 250, A). By the continued division of the inner 

 cells 100 to 150 cubical cells are formed, each of which con- 

 tains a single sperm-cell ; somewhat later the walls of the 

 cubical cells dissolve, and the sperm-cells become free in the 

 antheridial cavity, from which they are soon allowed to es- 

 cape by the separation of the apical cells of the enyeloping 

 layer {an, Fig. 250, A). At this time each sperm-cell con- 

 tains a spermatozoid, which soon escapes by the rupture of 

 the cell- wall. Each spermatozoid is a thick, spirally coiled 

 filament of protoplasm, tapering anteriorly, where it is pro- 

 vided with numerous cilia, which give it motility. 



Fig. 249.— Portion of the up- 

 right stem of Equisetum Td- 

 Tnateia (nat. size), i. i, inter- 

 nodes ; k, central hollow space 

 of internode ; I, air spaces (la- 

 cunae) in the cortex ; s, sheath 

 of united leaves ; s, their sep- 

 arate apices (teeth) ; a, a', a", 

 basal internodes of lateral 

 branches. — After Sachs. 



