Cavers : Sonre Points in the Biology of Hcpciticce. 1 7 1 



fibrous thickeniiii^s. Many of the cells contain brown spherical 

 or elong"ated oil-bodies, usually six or seven in each cell. These 

 bodies are evidently to be reg'arded as products of excretion ; 

 even after plants have been kept in total darkness for several 

 weeks the oil-bodies remain unchaiii^ed in the older parts of 

 the thallus, whilst the newly-formed branches contain them in 

 abundance. Oil-bodies are found in a larg-e number of Hepatica-. 

 and it has been found that they play an important part in the 

 economy of the plant bv rendering" the tissues distasteful to 

 snails and other animals, which rarely attack fresh plants, 

 though the\ will eat pieces which have been soaked in alcohol 

 to remove the oil and then washed in water. Very frequently, 

 the cells forming- the lower colourless portion of the thallus are 

 found to be traversed by fungfal hypha;, which ramify through 

 the cell-cavities and often bear swollen vesicles. The fungus- 

 infested or mycorhizal zone extends in the midrib to within 

 a very short distance of the g^rowing-point, and is especial!}- 

 well developed in the larg^er and more fleshy plants.* The 

 growing--point lies at the bottom of the deep notch found at the 

 anterior margin of each branch, and is occupied by a singie 

 larg-e cell, the apical cell, from which are cut off new cells that 

 give rise to the whole oi the tissues. The superficial cells in 

 this reg-ion g-row out to form club-shaped hairs, which secrete 

 mucilag-e, and this serves to absorb and retain moisture and to 

 prevent the delicate newh-formed tissues of the growing'-point 

 from becoming" dried up. 



Starting" from a relativelv simple form like Pc/Iiti, the 

 differentiation of the plant-body in the Hepaticai niay be traced 

 along" three diverging" lines, (i) The thallus remains simple in ex- 

 ternal form, but becomes differentiated internally and may attain 

 a hig"hly complex structure. Beg"inning" with Riccia, we have in 

 the Marchantiales a beautiful series of forms showing; g"radual 

 elaboration of the thallus. (2) The thallus remains simple as 

 reg"ards internal structure, but becomes difterentiated into a 

 cylindrical midrib and a single-layered wing on either side, e.g., 

 Mctzgeria. In some oi the forms belonging to this type, the 

 niidrib shows a well-defined strand of long narro'w cells with 

 pitted walls, having a remarkable resei"nblance to the vessels of 

 higher plants. The thallus may further become differentiated 

 into a cylindrical basal portion which is colourless or brownish, 



* The writer has recently observ'ed a well-developed mycorhizal zone in 

 Aiieura (>inguis, fresh material of which was kindly sent b\- Mr. I'. Farley, 

 oi Aberystwyth. 

 190.^ May I. 



