THE HIGHER CRYPTOGAM I A. 13 



matter, is formed above the young fruit, into which indi- 

 vidual cells of the adjoining tissue protrude in the form of 

 jointed hairs (PI. II, fig. 2). A wart-like elevation of the 

 upper side of the flat stem denotes the spot at which a 

 fruit-rudiment lies concealed within. Owing apparently to 

 the position of the archegonium {i. e., the young fruit), this 

 excrescence is always oblique to the fore edge of the shoot. 

 Eventually the growth of the fruit exceeds that of its 

 covering. One of the causes of this growth is an increase 

 in number (commencing at an early period, and continuing 

 until the bursting of the fruit) of those cells of its lower 

 portion which lie immediately underneath the basal enlarge- 

 ment ; or, in other words, a continually repeated division 

 of all the cells of one of the lower zones of cells. Another 

 cause of the growth of the fruit is an expansion of its cells 

 commencing at the apex of the fruit at the period when 

 the apical cell ceases to multiply, and extending slowly to 

 the base (PL II, fig. 5). The fruit breaks through the 

 arcuate lid of the surrounding cavity, and carries the 

 decaying tissue of the lid upwards, attached to the gelati- 

 nous mass which is accumulated above the apex of the 

 fruit, and which is traversed by the jointed hairs now 

 broken up into their individual cells ; it (the fruit) then 

 appears above the surface of the stem, apparently sur- 

 rounded by a sheath. The dome-shaped mass of gelatine, 

 covered with a brownish layer of cells, is the so-called 

 Calyptra of the earlier observers (PI. II, figs. 4, 5*). The 

 differentiation of the parts of the internal tissue of the 

 fruit begins shortly before the latter breaks through its 

 covering, and proceeds from above downwards. Certain 

 cells, forming an axile cylindrical string of from twelve to 

 sixteen rows of cells, one above another (each now showing 

 four cells in transverse section), cease to form horizontal 

 septa, whilst in all the other cells at least one more such 

 division takes place (PI. II, fig. 5). This string of cells 

 is the future columella. The layer of cells immediately 

 surrounding it is that out of which the spores and elaters 

 are developed, which extend from the columella to the 

 wall of the fruit. In this layer the multiplication of the 

 cells by division by horizontal septa is twice as active as 



