ALLEN— SEX INHERITANCE IN SPHyEROCARPOS. 297 



germinate, or that the sporeHngs growing from them had died. A 

 question mark ( ?) in the table indicates that no involucres had yet 

 appeared upon the plant in question, so that its sex could not be 

 determined. 



It is plain that all the cases shown in Table I., with the excep- 

 tion of the last four, harmonize with the expectation of two females 

 and two males. The last three cases can be made to harmonize by 

 the assumption made by Douin, namely, that two spore tetrads 

 germinating in close proximity may give rise to a group of eight 

 plants (or fewer), which will be expected to include four females 

 and four males. There remains one case (of three females and one 

 male) which does not agree with the expectation, unless it be 

 assumed to represent the four survivors of a group of eight. 



However, it appeared from this study, as well as from a more 

 extended observation of the behavior of plants in culture, that the 

 question of the sex potentialities borne by the spores can be finally 

 settled only by the use of more exact methods. The sources of 

 possible error are at least three : the impossibility of determining 

 with certainty just which plants have come from the spores of a 

 single tetrad ; the multiplication of plants as a result of their branch- 

 ing and the separation of the branches as independent plants, either 

 by accident or by the death of the older portions ; and the produc- 

 tion of new plants by regeneration. All these sources of error are 

 likewise present in the observation of plants growing in nature, 

 although the second is perhaps less important under these conditions 

 because of the slower growth out of doors. It is thus quite possible 

 that Douin's " abnormal " cases may not be real exceptions to the 

 general rule ; although, on the other hand, it must be admitted as at 

 least conceivable that in an occasional instance an error from one 

 of the causes mentioned might make a really aberrant case seem to 

 agree with the rule. The possibility of a modification of the appar- 

 ent sex ratio as a result of branching or of regeneration has recently 

 been recognized by Douin (C. and R. Douin, 1917). 



Attempts to develop better methods of studying this question 

 led to the sowing of isolated tetrads on various substrata. Diffi- 

 culties have been met with in securing favorable conditions for 

 germination and in preventing contamination, and the results thus 



