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1899] ORIGIN OF THE Le:AFY SPOROPHYTE 55 
organized for the fullest use of terrestrial conditions ; while the 
pteridophytes laid emphasis upon chlorophyll work, and became 
highly organized for terrestrial life. It would seem possible, 
therefore, with the three factors to take into account, that two 
distinct asexual lines may have been organized, distinct in the 
factor selected to dominate. 
Such a conception may be simple enough, but it is hardly 
worthy of consideration without more practical statement. If 
more favorable structures can be developed in response to the 
needs of spores or gametes, there seems to be no good reason 
why more favorable structures may not be developed in response 
to the needs of chlorophyll work. If such a response in struc- 
ture is possible, it would naturally express itself first in develop- 
ing the largest display of chlorophyll tissue in the most favor- 
able region of the body, which would gradually become 
differentiated more and more distinctly from the rest of the 
body. It does not seem clear why the appearance of an erect 
leafy axis, bearing neither gametes nor spores, is not quite as 
Supposable as the appearance of a sporophore with neither 
gametes nor leaves, ora gametophore with neither spores nor 
leaves. 
Of course such a leafy axis would be an integral part of the 
thallus body from which it was developed, and in no sense a 
distinct « generation,” any more than the leafy gametophore and 
the protonema of mosses are distinct generations. Upon such a 
leafy axis spores would find a more favorable position than upon 
the ordinary thallus body, and eventually they would be segre- 
gated upon the leafy axis, developing in connection with chloro- 
phyll tissue just as they had in the thallus body. In such condi- 
sons comparatively simple sporangia would be developed, being 
entirely subordinated to the nutritive tissues. A parallel case 
is found in the gametophore of mosses, which also prove favor- 
able for leaf development; or even in the sporogonia of certain 
ophytes, which also prove favorable for chlorophyll tissue, 
this 's rigidly subordinated to the work of spore production. 
With the development of a leafy axis bearing spores, there is 
