ECOLOGICAL ADAPTATIONS OF CERTAIN FERN PROTHALLIA 495 
group of prothallia averaged 2-4 mm. wide and showed earlier dead 
tissue and antheridia and archegonia long past mature (figs. 36, 37). 
The younger portions of these plants bore mature sex organs and in a 
few cases sporophytes of one or two leaves. The similarity of the 
younger plants in size and development to those in cultures from spores 
collected and sown September 4, just before the rain of September 12 
first made possible germination and growth in the field, leaves little 
room for doubting that these plants were produced by the germination 
of spores in the fall of 19 13. The plants of the second group were 
much larger than those of cultures started August 30. In fact they 
were quite similar in ever>' way to plants examined in April, 1914, of 
cultures started in September 1913 and allowed to remain out of doors 
during most of the winter of 19 13-14. Their age is evidenced by the 
dead basal areas. There are two possible explanations of the appear- 
ance of these plants. The first, that the plants grew from spores which 
had lain dormant through the winter and had germinated in the early 
spring of 1913, need hardly be considered, because no indications of a 
tendency to lie dormant has been found in experimental cultures, and 
because the growing season in the spring of 19 13 was too brief for the 
production of plants of the size found. The second possibility, and 
what seems to the writer the only plausible explanation, is that the 
larger plants were produced by the germination of spores in the 
autumn of 1912. This view includes the belief that the plants had 
survived the winter of 19 12-13 with a minimum temperature of 
— 23° C. in the field. The experimental data presented above have 
prepared the way for such a belief, and the finding of many living 
plants in late January, 1914, and even in April, makes the possibility 
of surviving the winter not only a belief but a certainty. The writer 
feels quite safe in saying that a considerable portion of the prothallia 
of this fern, grown from spores germinating in the late summer and 
autumn, live through the winter and produce sporophytes the next 
summer. 
The following facts touching the reaction to light have been 
noted in the field. The usual place of growth of prothallia is under 
old leaves in crevices in limestone or in depressions in the soil. Any 
chance breeze may by shifting the covering produce variations in light 
intensity equal to the widest range in the writer's experiments. In 
fact nearly all the facts of behavior noted in the experimental cultures 
have been verified in the field by the finding of forms from the branch- 
