TRAXSACTIONS OF SECTION K. 1037 



aposporous protonema: but that some such potentialities are there is in no way- 

 inconsistent with the antithetic theory. 



I have above pointed out how morphology has recently passed to an experi- 

 mental stage, and I am glad to say that by means of the cultures of Dr. Lang and 

 others we are beginning to gain an insight into the circumstances which lead to 

 these phenomena. In certain Ferns direct apogamy occurs ; that is, ' the imme- 

 diate production of vegetative buds by prothalli which are usually incapable of 

 being fertilised;' the origin of this is still obscure. But apogamy may also be 

 induced in various other species. Dr. Lang states that ' the causes which appeared 

 to induce apogamy in these prothalli were, the prevention of contact with fluid 

 water, which rendered fertilisation impossible, and the exposure to direct sunlight. 

 Possibly the temperature had some effect.' It is further to be noted that in every 

 case of induced apogamy ' normal embryos were produced when conditions per- 

 mitted fertilisation.' Now the conditions of prevention of fertilisation, exposure 

 to light, and possibly also a high temperature, all lead to a plethoric state, which 

 we may thus recognise as a precursor of induced apogamy, possibly also of apogamy 

 at large. 



On the other hand, the circumstances which precede or accompany apospory 

 are commonly those of deficient nutrition. In the case of Ugo Brizi's Funaria, it 

 is mentioned that the capsules were atrophied and buried in the soil, where they 

 could not obtain nourishment by their own assimilation. In the induced apospory 

 of Stahl and Pringsheim the growths appear upon parts of the chopped-up 

 seta, isolated from their usual sources of supply. Among Ferns, the conditions 

 of nutrition which precede apospory have not been noted in all cases ; but the 

 following facts are interesting. Athyrium Filix-foemina var. clarissima is a pale 

 chlorotic Fern with exiguous leafage, while the more or less complete arrest of the 

 sporangia is a concomitant of apospory. In Folystichum Angulare var. pulcherri- 

 onum there is no obvious disturbance of the vegetative organs, but I have specially 

 noted the sporal arrest, which, in the specimens examined by me, appeared to be 

 complete. This is, then, a concomitant of apospory, though it may be uncertain 

 how far there is a causal connection. In the case of apospory in Pteris aquilina, 

 reported by Farlow, there is an irregular diminution of leaf-area in the pinnules 

 which show apospory ; this is accompanied by various stages of abortion of the 

 sporangia, though some fully-matured spores were found. Here, as also in 

 Folystichum uvyulare, the tips are specially affected. Farlow remarks, 'the 

 sporangia became more and more irregular the nearer they were to the tip.' In 

 the case of Scolopendrhnn vulgare, the plants which showed apospory at so 

 peculiarly early a stage had been raised by Mr. Lowe from prothalli which had 

 been repeatedly divided, a process calculated to affect the physiological condition. 

 The aposporous plants of Trichomanes alatum, pyxidiferum, and Kaulfussii, were 

 all cultivated under artificial conditions, and are characteristically shade-loving 

 plants, a habit which must aflect their nutrition. Perhaps the most interesting 

 case, however, is that described by Atkinson in Onoclea. In plants from which, 

 by removal of the foliage leaves, the sporophylls had been induced to change their 

 character and develop as foliage leaves, the sori were arrested. ' When the leaf 

 has lost so much of its reproductive function that the sporangia are becoming rare 

 or rudimentary in the sorus, apospory frequently occurs, and the placenta develops 

 among the rudimentary sporangia prothalloid growths.' Here is, again, a case of 

 deficient nutrition ; the assimilating leaves, after formation, but before they could 

 have carried their functions far, were removed. The plant makes an effort to 

 supply their place at the expense of spore-production ; arrest of sori and sporangia 

 •is the result, accompanied by cases of the direct vegetative transition to the 

 prothallus. From these examples we see that deficient, or, at least, disturbed 

 nutrition is frequently, perhaps always, a concomitant of apospory. Thus there is 

 some countenance for the view that apospory and apogamy follow on converse 

 conditions of nutrition. 



We may next inquire how these converse conditions may lead to the changes 

 in question ; and especially the state of the nuclei ought to be considered. Owing 

 to practical difficulties of observation the behaviour of the nuclei in apogamy 



