■566 Black : The imbedded antheridium in Dryopteris 



present a remarkable mobility. As dryness and the exposure to 



direct sunlight were the only cultural changes from the normal 



state, the results obtained may be attributed to those causes, none 

 of these structures being found in the normal control cultures. 



The fact that one form of the expression of the potentialities of 

 these prothallia is that of a deep-seated antheridium is of interest 

 from a number of standpoints. Morphologically the imbedded 

 antheridium is interesting, in that its origin and development is 

 very similar to the origin and development of the normal anther- 

 idium of a much lower order of ferns. The detailed development 

 of the antheridium in the Ophioolossaceae (Campbell '07) is 

 essentially similar to the development of the imbedded antheridium 

 as found in Dryopteris stipidaris. The position of these antheridia 

 in the actively growing part of the prothallium is evidence of the 

 manifestation of an active response to a forced environment and 

 not a condition due to degeneracy or a reversion to more primitive 

 characters. The presence of normal antheridia on the same pro- 

 thallium bearing the imbedded kind shows that, while the condi- 

 tions are equal for producing either, the condition of dryness is 

 essential for the formation of the deep-seated antheridium. The 

 imbedded antheridium in the dry cultures was not an occasional 



■ ■ 



occurrence, as one and frequently two or three were found on the 

 majority of the prothallia. 



That the response to this dry condition was the production of 

 imbedded antheridia, shows the far-reaching effect of such an 

 environment, as well as the success of the prothaHii in combat- 

 ing it. A superficial organ on a prothallium grown in dryness is 

 more in danger from drought than one deeper in the prothallial 

 tissue. To protect the antheridia from the disasters of drying out 

 and thus becoming incapable of functioning, an antheridium has 

 been developed, completely imbedded in the prothallium. Deep 

 seated in its origin and development, such an antheridium is pro- 

 tected from the effects of drought, obtaining from the surrounding 

 prothallial cells the maximum amount of moisture supplied the 

 plants. The improbability of a sperm from a superficial anther- 

 idium reaching an egg is apparent in these prothallia due to the 

 lack of the necessary medium, i. e., water. If there could be an 

 internal way for the sperm to reach an ^g^, another suggestion of 



