the Embryos and Seedlings of the Cactaceae . 429 
desert-station is essential ; and after the tropical gardens 
have been provided for, this may well next attract the 
attention of botanists. 
Germination. 
The present study properly begins with the fully formed 
embryo in the ripe seeds. The development of the embryo, 
of the ovule, and of the fruit, is a distinct question on which 
I expect to make another communication later. The subject 
has already received some attention from Planchon 1 , Payer 2 , 
Guignard 3 , d’ Hubert 4 , but the results are too fragmentary 
to be of use in this study. In general the seeds in the 
Cactaceae contain a curved embryo with but a slight quantity 
of albumen lying against its concave side. 
In the germination of the seeds I have seen little that is 
especially remarkable. On absorption of water the seed-coat 
is either split open along a part of its length, as in Opuntia ; 
or a piece is pushed off valve-like from the micropylar end, 
as in Echinocactus , Cereus , &c. In the latter cases, and no 
doubt in many others, this is effected by the great swelling 
of a ring of epidermal cells at the lower end of the hypocotyl, 
which form a distinct ridge or collar from which later the 
hair-collar develops. This swelling is common in other 
families, and no doubt forms the basis of the well-known 
< wurzel-hals,’ or ‘ haftscheibe.’ Klebs has correctly described 
the nature of the germination in this family ; it belongs 
distinctly to his fifth type, those with the main root growing 
little or not at all during germination, with a crown of long 
root-hairs on the swollen base of the hypocotyl, the hypocotyl 
lifting the cotyledons out of the seed to above ground. In 
the latter respect this account is not strictly accurate for this 
family, for the seed-coat is commonly carried up on one 
of the cotyledons, no doubt to allow of the absorption of the 
1 Ann. Sci. Nat., Bot., 1845, 275— 31; i. 
3 Bull. Soc. Bot. de France, XXXIII. 
2 Ann. Sci. Nat., Bot., 1872. 
4 Ann. Sci. Nat., Bot., 1896. 
