l60 COOK 



of asexual propagation. It can be shown, however, that this 

 implication is not necessary, and that apospory need not inter- 

 fere with the formation of sex-cells, nor with the continua- 

 tion of truly sexual methods of reproduction. The elimination 

 of the spores does not require that the fusion of chromatin 

 (mitapsis) which must precede the formation of new sex-cells, 

 shall also be omitted ; it may be merely deferred and passed 

 along to later generations of cells. If instead of occurring in 

 the body of the parent plant, mitapsis were carried over into 

 an aposporous female prothallus and thus approximated in time 

 to the formation of the sex-cells we would have a condition 

 similar in all important respects to the reproductive system of 

 the angiosperms. 



The whole group of the archegoniate plants affords a con- 

 spicuous instance of such deferment of mitapsis into later and 

 later cell-generations, instead of taking place in the fertilized 

 egg-cell as in the lower algae. Unless mitapsis had been de- 

 ferred the larger " sporophytes " and increasingly abundant 

 sporogenous tissues which characterize the various families of 

 archegoniates could not have developed. A still further post- 

 ponement of mitapsis, combined with apospory, is therefore 

 entirely in accord with the general course of evolution already 

 followed by the group from which the primitive angiosperms 

 are now commonly believed to have arisen. 



THE VEGETATIVE CAPSULE OF ANTHOCEROS. 



Anthoceros is a thallose liverwort which has been accepted 

 by some as representing a primitive ancestor of the ferns, but 

 which may be used with greater propriety to illustrate a stage 

 in the development of the angiosperms. 



Until fruiting begins, a plant of Anthoceros consists merely 

 of a thallus, or plate of slightly differentiated cells, lying flat 

 on the surface of moist soil. The fruiting part of the plant is 

 an upright, cylindrical, two-valved capsule. The outer walls 

 of the capsule consist of flesh}^, green tissues, like those of the 

 thallus, and similarly endowed with the power of vegetative 

 growth. This vegetative capsule is even provided with special- 

 ized breathing-pores, though the thallus is without stomata. 



