THE BRYOPHYTA 125 



SUMMARY 



We have now completed the simple life-history of 

 this Liverwort. We must not suppose that all Hepaticse 

 are equally simple ; the class is a large one, said to include 

 nearly four thousand species, and embraces a considerable 

 variety of form and structure. In some (e.g. Marchantia) 

 the thalloid form is retained, but a great complexity of 

 anatomical structure exists, while at the same time the 

 thallus bears highly-modified branches for the produc- 

 tion of the sexual organs. Special organs of vegetative 

 propagation gemmae are also very frequently present, 

 which serve to reproduce the thallus directly. In 

 another very numerous series of Liverworts, we find, 

 instead of a thallus, a delicate leafy stem of great 

 beauty; in this group (which includes the majority of 

 the species) we have a high external differentiation of the 

 oophyte, while the anatomical structure remains simple. 

 We will now, however, sum up the essential points in the 

 development of Liverworts, as represented by our type. 



The thallus of Pellia is obviously comparable to the 

 prothallus of a Fern, while the antheridia and archegonia 

 also are evidently of the same nature as the sexual organs 

 of the Vascular Cryptogams. Fertilisation is accomplished 

 in just the same way, but the product is totally different. 

 In the Ferns the sexually produced embryo grows up into 

 the plant itself, which goes through a long and vigorous 

 course of purely vegetative development, before it 

 proceeds to form the asexual reproductive cells (spores). 

 In Pellia, and Liverworts generally, the sexually pro- 

 duced embryo grows, not into a plant at all, but merely 

 into a fruit, which remains all its life attached to and 

 dependent upon the sexual individual. The capsule, it 



