302 TltANSAUTlONS AND PROCEEDINGS OF THE [Sess. LXiv. 



conditions of life. Part of the sporogenons tissue has 

 been sterilised to act as an envelope to the rest. In 

 such a type as this, t'.//. Riccia, the envelope may be 

 taken as the hrst rudiments of a vegetative system. The 

 advance on the Colcochatc type is, however, very slight, 

 and the development of the sporogenous and tlie vegetative 

 tissues are practically contemporaneous. With the rise 

 of tlie sporophyte, the vegetative system becomes better 

 differentiated, and of progressively greater physiological 

 importance, and according to Mehnevt's principle its 

 development is accelerated. Thus, in such forms as 

 Marchantia, Pellia, and so forth, an important vegetative 

 organ — tlie foot — appears, and develops somewhat before 

 the sporogenous tissue ; a " time displacement " in the form 

 of an acceleration of development has occurred, concurrent 

 with the increase in importance and the greater differen- 

 tiation. 



Vegetative differentiation and physiological importance 

 of the vegetative system are more marked in Anfhoccros, 

 and there is a corresponding acceleration in the develop- 

 ment of the. vegetative system. The vegetative system 

 comprises the foot, the columella, and the envelope of 

 the .sporogonium, which is chlorophyllous and has stomata,. 

 the meristem, etc. Of these, the columella and the foot 

 are developed before the sporogenous organs. While the 

 greater part of the vegetative system has outstripped the 

 sporogenous system in its rate of development, part is 

 contemporaneous with it. 



In the Mvsci, with the vegetative system differentiated 

 into absorbent and conducting parts — foot and seta, and 

 assimilating organ — apophysis with chlorophyll and stomata, 

 conspicuous in the Splaclmnms (Vaizey, 10), the same 

 acceleration in the rate of development is seen as in the 

 higher Hepatiac, — the sporogenous tissue on the whole 

 developing late (Campbell, 10). 



Arrived at "the highest type of Jh-ijuiiliylK, we are con- 

 fronted by a wide gap. It is a long cry from even 

 the most developed sporogonium of a Jir]jo])]iyie to the 

 sporophyte of the simplest Vafsndar (Jryjjtoyam. Our 

 appreciation of the width of the gap is emphasised on 

 remembering that while on the one side, as sporophyte,. 



