LEPIDOCABPON AND SPENCERITES 



35 



spores is the result of lack of an effec- 

 tive mechanism for bursting open the 

 sporangia, such as is present, for ex- 

 ample, in Selaginella (Mitchell, 1910). 

 Despite this, the essential free-sporing 

 adaptations are not materially altered 

 in Mazocarpon. The thickness of the 

 megaspore coats indicates that the nutri- 

 tional bond between sporophyte and 

 gametophyte was not any greater than 

 in other free-sporing plants. The oc- 

 currence of intrasporangial tissue has 

 no essential bearing on the question 

 since it has no effective connection with 

 the mature growth of the gametophytes. 

 The writer considers that the intraspor- 

 angial tissue served no essential protec- 

 tive or nutritive function after forraa- 

 tion of the spore coat. Any effect the 

 persistent intrasporangial tissue may 

 have had on spore distribution is that 

 which would result in any free-sporing 

 plants with poorly dehiscent sporangia. 

 There seems to be no valid reason why 

 these megaspores or sporangia should 

 be termed ^'seed-like". Such a designa- 

 tion merely confuses the useful distinc- 

 tion between free-sporing and seed- 

 bearing plants. 



Mazocarpon and Lepidocarpon 



On the other hand, the lepidocarps 

 have every claim to recognition as true 

 seeds because they possess all the phys- 

 ical and physiological attributes of the 

 seed habit. The lepidocarp megaspor- 

 angium is indehiscent. The seed mega- 

 spore is greatly enlarged, the megaspore 

 membrane is modified for facile inter- 

 change of food materials and has lost 

 its original essential function as a pro- 

 tective membrane just as much as in 

 any of the Paleozoic gymnospermic seeds. 

 The sporophytic structure is specialized 

 to form a protective integument, and the 

 sporophyll lamina is probably effective 

 as a dispersal mechanism. The distinc- 

 tive feature of Mazocarpon, viz. the ex- 

 traordinary development of intrasporan- 

 gial tissue (function unknown) is not 

 characteristic of Lepidocarpon or of 

 Lepidostrohus. The most distinctive fea- 

 ture of Lepidocarpon, the elaboration of 

 an effective integument, is not suggested 

 by either Mazocarpon or Lepidostrohus. 

 Although it has often been overlooked, 



Scott pointed out that the integument 

 of Lepidocarpon appears as a new organ 

 and cannot be interpreted as a mere up- 

 folding of the lateral wings of the pedi- 

 cel. That this was a correct interpreta- 

 tion is borne OLit by the study of Illinio- 

 carpon in which the integument is still 

 further elaborated and is entirely dis- 

 tinct from the sporophyll lamina. 



Miss Benson further confused this 

 issue when she suggested (Benson, 1920) 

 that Cantheliophorus Bassler (1919) 

 was identical with Sigillariostro'bus and 

 compared favorably with Mazocarpon. 

 Recent studies (Schopf, 1940, 1941) in- 

 dicate that Ccmtheliophorus Bassler 

 shows the seed megaspores and integu- 

 ments which characterize the genus 

 Lepidocarpon and, despite the differ- 

 ences in preservation, should be identi- 

 fied with it. The relationship of Can- 

 theliophorus and Sigillariostrohus is en- 

 tirely indirect. 



The relationship between seed-bearing 

 Lepidocarpon and essentially free- 

 sporing Mazocarpon can not be re- 

 garded as direct. The two are more 

 reasonably interpreted as divergent spe- 

 cialized reproductive types among the 

 Carboniferous lycopods. Miss Benson's 

 statement (1918, p. 582) that ''3Iazo- 

 carpon is exactly intermediate between 

 Lepidostrohus and Lepidocarpon'^ is 

 without basis either as an analogy or 

 homology since entirely diverse speciali- 

 zations distinguish the two groups. Both 

 were coexistent over a long period of 

 geological time. Lepidocarpon wildia- 

 num was described from the Calciferous 

 Sandstone of Burntisland by Scott in 

 1901, and Walton (1936) has recently 

 mentioned the occurrence of Lepido- 

 carpon in beds of the Lower Carbonifer- 

 ous Cementstone group from the Isle 

 of Arran. It thus at least equals and 

 may even antedate the existence of both 

 Mazocarpon and Sigillariostro'bus. 



Mazocarpon and Spencerites 



The resemblance of Mazocaiyon oedip- 

 tcrnum and plants classified as Spencer- 

 ites is interesting chiefly because of the 

 obscurit}^ of the affinities of Spencerites. 

 However, despite these similarities, there 

 is no proof of a direct relationship be- 



