13 ° Johnson . — On the Development of the 
behaviour is apparently analogous to that of certain marginal 
cells of the fifth grade in the leaf. 
When the second sporocarp of a pair is formed, it arises 
usually from a marginal cell of the second or third segment 
of the first sporocarp on the side of the latter toward the 
petiole on which it is borne ( F 2 , Fig. 26), and a third probably 
arises in the same way from the second. The position of the 
apical cell of this second sporocarp, with reference to the first, 
is transverse, like that of the apical cell of the first with 
reference to the petiole. This mode of origin of the younger 
sporocarp from older ones shows that the common stalk of 
the pair is simply the portion of the stalk of the older one 
below the point of origin of the second, and the same is true 
of the stalk common to the second and third sporocarps of 
a trio. It is probable that where two or more sporocarps 
are inserted on the petiole by separate stalks, as happens 
occasionally in M. qtiadrifolia> and constantly in forms like 
M ’. polycarpci, we should find them to originate from marginal 
cells of successive segments of the petiole, but the early 
stages of this type were never seen. 
The Stalk. 
The further development of the seven divisions of each 
segment mentioned above differs in the different regions of 
the sporocarp. In the four or five oldest pairs of segments 
that form the stalk, their later history is very like that of the 
segments of the petiole, except that the axial bundle is here 
formed entirely from the plerome of sections I and II and 
a part only of that from section III. All the remaining 
portions of these segments, and all of the other segments, 
give rise to mesophyll and to hypodermal and epidermal 
structures, but no tannin-sacs are formed among the 
mesophyll-cells, and only very small air-canals between these 
and the hypodermis. A structure is thus formed of smaller 
diameter than the petiole, and of much firmer tissue, which 
swells out at the upper end (/. t., Fig. 44) to form the lower 
tooth of the capsule. 
