THE SHOOT. 83 



99. The sporophyte shoot.- -The shoot developed by the 

 sporophyte of mosses and liverworts forms no leaves, but 

 develops as a slender cylindrical stalk, at the distal end of 

 which the capsule containing the spores is formed (figs. 64, 

 73). It is rather difficult to see in this cylindrical stalk the 

 homologue of the leafy stem developed by the sporophyte of 

 the fernworts ana other plants. 



The simultaneous performance of the work of nutrition and 

 of sexual reproduction proved impracticable, as shown by the 

 development of the liverworts and mosses, which are all 

 humble plants. The fernworts, originating probably at an 

 early period from the same ancestors as the liverworts, sep- 

 arated the two functions and laid the chief work of nutrition 

 upon the sporophyte. The advantage thus gained enabled 

 the extinct fernworts to develop into plants of tree-like size, 

 and to become the ancestors of all the seed plants. 



The gametophyte shoot was, comparatively, a failure; the 

 sporophyte shoot was a marked success. It has become 

 adaptable to many conditions and many functions. To 

 accomplish this its members have been extensively modified 

 in form and structure in various plants. The development 

 and mode of branching, together with the various forms 

 which the shoot assumes, are now to be discussed, to be fol- 

 lowed by an account of the two members, stem and leaf, into 

 which it is usually differentiated. 



100. Primary shoot.- -The shoot which develops from the 

 fertilized egg is called the primary shoot. A very few excep- 

 tional plants are found in which no primary shoot develops, 

 although there are a number of cases in which the primary 

 shoot becomes early aborted, and its place taken by secondary- 

 shoots arising from the root. The primary shoot normally 

 arises in fernworts from the anterior half of the egg. The 

 anterior hemisphere usually divides into two quadrants, one 

 of which develops into the primary leaf, and the other into 



