32^ 



W. PEAESON ON THE MOEPHOLOGT OF 



* 



99 



tropbophyte found in Welwitschia. There are therefore two questions concerned here, 

 of which the more comprehensive is that of the relation of the endosperm of Welwitschia 

 to that of the Angiosperm. The force of any argument based upon Welwitschia alone 

 could not hut be diminished by the aberrant character of the genus. It might be urged 

 that the manner in which the endosperm was formed was but a link in a chain of 

 adaptations to peculiar conditions. Tiie occurrence of the same type of endosperm in 

 Gnetum is a fact which must be accorded great weight in any view that may be taken. 

 This interpretation of the WelicitscMa endosperm has been discussed by Lotsy 

 After giving a brief outline of the hypothesis referred to in the last paragraph, the 

 author says :— " Was ist nun der Grund, dass Pearson bei WelicitscMa die Kerne des 

 Embryosackes, trotzdem sie, ebenso wie bei alien anderen Gymnospermen, aus wieder- 

 holter Teilung des Macrosporenkernes entstehen, nicht als Prothalliumkerne sondern 

 als Gametenkerne aufiFassen will ? Der Grand ist 



w 



" {a) dass die des oberen Teiles befruchtet werden ; 



" ip) die des unteren Teiles miteinander fusionieren konnen 



With regard to the latter (6), Lotsy very truly remarks that it is "kein triftiger 

 Grund." It may be admitted, without further question, that the fact of fusion does not 

 in any way help us to determine the nature of the nuclei which enter into fusion ; nor, 

 in fact, was it ever put forward as having any bearing upon the question. These nuclei 

 would have been regarded as gamete-nuclei if they never fused. 



The other reason given by Lotsy (a), which he describes as " eigentlich nur ein Spiel 

 niit Worten," is more to the point, though, standing by itself, its meaning and force 



are not clear. 



On the previous pagef Lotsy admits that *'alle Kerne im Embryosack von Welwitschia 

 homolog sind." Therefore, if the nuclei of the micropylar region of the sac are gametes, 

 as they undoubtedly are, the free nuclei of the lower region, which normally fuse to form 

 the nuclei of the primary endosperm cells, may be sexual also. The reasons for regarding 

 them as sexual, which were given in detail J, may be repeated here, omitting the first 

 three, since the homology is admitted : 



4. When septation is completed some compartments contain few nuclei (six or 



less) ; others a larger number. The latter are normally confined to the lower 

 three-fourths of the sac ; the former may occur anywhere, though they usually 

 fill the upper fourth of the sac and are either absent from or much less 

 abundantly developed in the lower three-fourths. 



5. In compartments containing less than six, wherever they may be situated, the 



nuclei do not fuse, but remain free; these are functional gametes, fusion 

 occurs only in those compartments in which the nuclei are in greater number ; 



a sterile tissue is thus formed. 



6. In an abnormal case in which the upward growth of the sac was impeded by a 



second one above it, compartments which normally would have contameu 



• 



Lotsy, 1911, p. 340. t Lotsy, 1911, p. 339. % Pearson, 1909, p. 378. 



