- Orchid Mycorrhiza. J. Ramsbottom. « 51 
fact Stahl considered that from this point of view the latter 
family are as important as the Orchidaceae. Moreover, in these 
families the seeds are small and numerous, with little reserve 
food material and no chlorophyll. Further there are the typical 
gradations from green plants to colourless saprophytes and 
correlated with this is an increase in number and decrease in 
size of the seeds, with a change in the embryo until we end in 
the most reduced examples with little differentiated or formless 
masses, and an increasing amount of fungus in the roots. The 
seeds of the saprophytic genera have a net-work. integument 
and in appearance bear a very close resemblance to those of 
orchids. The Burmanniaceae are closely related to the Orchida- 
ceae, and we should expect that showing so many characters 
in common there would also be a resemblance in the important 
one of obligate fungal infection for germination. In the Gentiana- 
ceae there are many isolated records of difficulties in obtaining 
seed germination in some of the genera, and it is common 
knowledge that many Gentians are difficult to raise from seed. 
It would seem extremely probable that in this family also the 
mycorrhizal fungus is necessary for seedling development. 
Ceillier* has worked out in detail the relation between the 
presence of mycorrhiza and small seeds. In certain cases asin 
Juncaceae the seeds are small and little differentiated, but as 
they possess chlorophyll they are able to begin photosynthesis 
immediately on sowing. Small seeds with much reduced embryos 
also occur in parasitic forms such as Cuscuta, Orobanche, etc. 
No fungus is present in these genera, but apparently germina- 
tion is not successful unless contact is made with the organs of 
the requisite host. It may be that the stimulus necessary in 
these cases is analogous to that requisite to bring about root 
formation in plants with obligate mycorrhizas. 
ORIGIN OF SAPROPHYTISM. 
What is the trend of evolution in plants of which the roots 
are normally infected with endophytic fungi? A general survey 
of families in which endotrophic mycorrhizas are typically de- 
veloped shows that it is the rule for these families to have small 
seeds ill-adapted for successful germination. It has also been 
proved for orchids and for Calluna that the seeds need to be 
infected by the mycorrhizal fungus before the seedling can 
of very special surroundings. Probably the fungi which are found in the roots 
in symbiosis are essential. The smallness of the seeds allows of a large number 
being formed, and thus the probability that one of the seeds at least will 
reach favourable conditions for germination is increased,’’ Goebel, Organo- 
graphy of Plants, Part II, pp. 254 [1898] 1905. 
* R. Ceillier, Recherches sur les facteurs de la répartition et sur le rdle des 
mycorhizes. Thése, Paris (1912), 
4—2 
