EQUISETACEsE 105 



the mode of development and structure of the archegones of Equisetum 

 differ in no essential respect from those of other Vascular Cryptogams. 

 The basal cell is wanting, and the neck-canal-cell does not extend the 

 whole length of the neck. The lower portion of the neck and the venter 

 remain completely imbedded in the tissue of the prothallium, while the 

 outermost or stigmatic cells of the neck lengthen greatly, and ultimately 

 bend outwards, giving to the archegone, when ready for impregnation, 

 the appearance of a miniature four-armed anchor. 



Although the prothallium of Equisetum is normally dioecious, it 

 is not very uncommon to find a few archegones on male, and a few 

 antherids on female prothallia. The abnormal sexual organs then 

 generally make their appearance later than the normal ones. 



The mode of formation of the embryo from the impregnated oosperm 

 is essentially the same as in other classes of Vascular Cryptogams. The 

 first division-wall is vertical to the axis of the archegone, and therefore 

 parallel to the surface of the prothallium ; by subsequent walls a division 

 takes place into octants. Of the four quadrants of the upper half, one 

 gives birth to the rudimentary stem, with a triangular pyramidal apical 

 cell, while from the three others proceed two cotyledons, which at a very 

 early period unite in their growth with the first leaf which proceeds from 

 the apex of the stem. From the lower quadrants of the octant are 

 formed \hefoot and the first root. The first few stems of the sporophyte 

 generation are successively thicker, and with a larger number of teeth 

 in their leaf-sheaths, until ultimately mature stems are produced from 

 perennial underground rhizomes. 



The stem of Equisetum always consists of very distinct more or less 

 elongated internodes, which are hollow, but are closed above and below 

 at the nodes by transverse septa or diaphragms. The cortex of each 

 internode is continued upwards above its upper node into a leaf-sheath, 

 which embraces the base of the next internode above, and is split at its 

 margin into teeth, varying from three or four to a considerable number. 

 From each tooth of the leaf-sheath a ' vascular ' bundle descends verti- 

 cally as far as the next node. The teeth at each node always alternate 

 in position with those of the leaf-sheaths belonging to the nodes next 

 above and next below it, and each descending bundle branches at the 

 node into two short diverging arms, each with its own xylem and phloem, 

 by means of which it unites with the two adjacent bundles of the next 

 internode below, where they descend into it from the sheath-teeth in 

 which they originate. In addition to the large central cavity in the axis 

 of each internode, the cortical tissue contains a number of much smaller 

 cavities running vertically through the internode, the lacunce or valle- 

 cular canals, which alternate with the * vascular ' bundles, and are there- 



