THE Bin OP/I VTA 323 



Fertilization is probably offocted rather rarely, owing to the 

 fact that an abundance of water is necessary in which the sperms 

 may swim about. Perhaps as a result of this we find many 

 devices among the mosses by which asexual reproduction is 

 effected, and most of the new individuals produced probably 

 arise by this means. 



Despite its large size and relatively high specialization, the 

 mosses are not believed to have led directly to any of the higher 

 plant groups, but we look instead to such simpler forms as 

 Anthoceros for a suggestion as to how the great gap which now 

 exists between bryophytes and pteridophytes may have been 

 bridged. 



QUESTIONS FOR THOUGHT AND DISCUSSION 



748. What great change in the character of the spores occurs as we 

 pass from algae to bryophytes? 



749. What is the advantage of a multicellular sexual organ over the 

 primitive unicellular type? 



750. What reason can you suggest for the presence of the ventral 

 canal cells and the neck-canal cells in the archegonium? 



751. What exceptions are there to the general rule that the thallo- 

 phytes have unicellular sexual organs? 



752. Where else in the plant kingdom below the liverworts have we 

 found dichotomous branching? Do you think that it is primitive or 

 not ? How does it differ from the typical branching of the higher plants ? 



753. Of what advantage to the moss plant is the seta? 



754. Why do you think it is that the bryophytes have never been 

 able to produce plants of any great height? 



755. In bryophytes, what are the advantages and the disadvantages 

 of the thallus type and of the leafy type of plant? 



756. In the general character of their thallus, what group of algae 

 do the liverworts most resemble? 



757. Why do you think it is that the liverworts are largely eoufined 

 to moist places, while the mosses often thrive in relatively dry ones? 



758. AMiat notable resemblance is there in structure between the 

 thallus of the liverworts and the leaves of the higher plants? 



