DEVELOPMENT OF PLANTS 



289 



(Fig. 196). In other genera there are indications of a Icjljin^^ in 

 the thallus which becomes more pronounced in some forms and 

 leads by gradual gradations to genera in which the lobes appear 

 as distinct leafy organs arranged in two rows upon a stem-Hke 



Fig. 197. One of the leafy Jungermanialcs, Porella: A, branch of the 

 plant bearing several sporophytes. B, under surface of a branch, showing 

 the lobing of the leaves and a row of minute scale-hke leaves. C, portion 

 of a branch bearing an archegonium surrounded by cup-like perianth with 

 minute involucrate leaves at base. D, branch with cone-like anthcridial 

 branchlets. At the left a single leaf is shown with globular antheridium 

 in its axis. E, section of a branch similar to C. The archegonium is seen 

 surrounded by the perianth and below the involucrate leaves. The sjxjro- 

 phyte is nearly mature and ready to elongate. It consists of a round cap- 

 sule containing elaters and spore mother cells that are dividing to form four 

 spores each. Below the capsule is the stalk or seta which ends in a foot 

 buried in the tissues of the branch. At the right is an unfertilized arche- 

 gonium that shows the original position and size of this organ. — H. O. Hanson. 

 19 



