Discussion on “ Alternation of Generations 115 
—the sporogonium of the Moss, with no roots, never became free, 
while the sporophyte of the Ferns, after a nursing period, protruded 
a root and became independent. In the light of Dr. Lang’s remarks, 
we might perhaps regard the two series as coming from two different 
ancestors, the one rootless before retention occurred, the other 
having already developed the habit of rooting. Tbe old memory of 
rooting would again obtrude itself and the condition for the evolution 
of the complex sporophyte be established. 
Dr. Lang had alluded to the reciprocal relation of the sporophyte 
with the retaining generation. To think of the resulting development 
of the maternal tissue as a “ gall ” seemed not unhelpful. The 
10.o seed and many other structures might then be interpreted as 
galls. If we could understand how gall-structures came to be 
part of the transmissible heritage of plants, much light would be 
thrown on seed and carpellary structures, and, lower down in the 
scale, on those peculiar structures in the Jungermanniaceae, called 
marsupia, which were quite seed-like in some respects. Unless we 
had some definite light on fixing transmission of this kind, we should 
have to wait a long time for experimental data. The effect of galls 
on vegetative structure was very striking ; Uromyces on Euphorbia 
Cyparissias modified the whole appearance and life of the plant and 
inhibited reproduction.’ He thought that a carefully thought-out 
series of experimental investigations into the conditions of gall 
production, might throw some light on the subject of that night’s 
discussion. 
Mr. A. G. Tansley said that he did not propose to detain the 
Society long, for he had nothing of any value to add to the remarks 
that had already been made on Dr. Lang’s striking contribution 
to morphological theory. As a matter of fact he had no particular 
claim to speak on the subject at all, for he had made no special 
study of any of the phenomena involved. The suggestion that he 
should speak that night presumably arose from the fact that he had 
recently had occasion to enter that highly speculative field, because 
his studies on the vascular anatomy of the Ferns had forced him 
to consider the problem of the morphological nature of the fern- 
frond, and thus, in its turn, the problem of the origin in descent of 
the Pteridophytic sporophyte—whether it was really to be regarded 
historically as an elaborated fruit-body, as he had been brought up 
to believe, or as a plant-body ultimately derived from an algal 
thallus. Into this highly obscure region of morphological specula¬ 
tion, with a minimum of facts that were really relevant and could 
be treated on a sound comparative basis, he had accordingly made 
an expedition, with the result that he had stumbled about in 
the very dim light, fumbling after half-seen objects in a feeble kind 
of way, and he certainly did not escape without bruising his shins. 
Upon the obscure mass of phenomena involved in this field 
Dr. Lang had now turned a light which he thought they all hoped 
might prove the searchlight of truth rather than the ignis fatuus 
of vain speculation. The hypothesis seemed a very promising one, 
and in accord with all the main classes of relevant phenomena. 
Its great merit, as the author had remarked, was that it appeared 
to be open to the test of experiment, and he did not see any reason 
why they should not have good hope that persistent and well 
conceived practical tests would eventually bring them to a sure 
conclusion as to its validity. Though they might never live to see 
