37(3 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
B. CRYPTOGAMIA. 
Cryptogamia Vascularia. 
Structure of Isoetes.* — Mr. J. B. Farmer lias subjected both the 
sporophyte and the oophyte of Isoetes lacustris to a careful examination. 
He shows that the statement of Hofmeister and others that the apices of 
the stem and root grow by means of apical cells, is founded on a mis- 
conception of the structure. Also that the existence of a ligule in both 
Isoetes and Selaginella must not be taken as indicating a close affinity 
between these two genera. The mature structure of the ligule is different 
in the two genera, and that of Selaginella arises from a multicellular 
protuberance, not from a single cell as in Isoetes. 
As regards the structure of the oophyte, the author differs from 
Pfeifer’s view, who regards the upper small-celled portion of the products 
of division of the megaspore, above the first diaphragm, as constituting 
by itself the prothallium, and compares the lower and looser mass of cells 
below the diaphragm to the endosperm of Angiosperms. Farmer maintains 
that they are both parts of the true prothallium, the former being the 
specially reproductive, the latter the specially nutritive portion of that 
structure. He then further traces the resemblance between the processes 
which take place within the megaspore of Selaginella and Isoetes , and 
those which occur in the embryo-sac of Angiosperms. 
Stem of Eqmsetacese.f — M. P. Yan Tieghem proposes a rearrange- 
ment of the species of Equisetum according to the characters derived by 
Pfitzer from the endoderm (Schutzscheide) under five types, viz. : — 
(1) Special endoderms in the rhizome and aerial stem ( E . limosum , 
litorale , giganteum, pyramidale , debile , Martii , xylochsetum ) ; (2) Special 
endoderms in the rhizome, two general endoderms in the aerial stem 
( E. hyemale , trachyodon , ramosissimum , myriochsetum , robustum , Isevigatum , 
Schaffneri ; (3) Two general endoderms in the rhizome and in the aerial 
stem ( E . variegatum ) ; (4) Two general endoderms in the rhizome, one 
general external endoderm in the aerial stem ( E . sylvaticum ) ; (5) One 
general external endoderm in the rhizome (E. arvense , maximum , pratense , 
palustre , scirpoides , bogotense , diffusum). 
The pericycle, which is always present aud always simple, follows 
step by step the endoderm in all its modifications ; and there are there- 
fore three general types of pericycle and endoderm, viz. — (1) Special 
pericycles and endoderms; (2) two general pericycles and endoderms; 
(3) one distinct general external pericycle and endoderm. It is only in 
the first of these three modes that the stem possesses its typical structure, 
identical with that met with in many Phanerogams. In the second 
mode the structure is still astelic (without central cylinder) ; but there 
is lateral fusion of the pericycles aud endoderm, although not always of 
the vascular bundles ; and this may be termed gamodesmic in contrast to 
the typical dialydesmic structure. In the third mode the structure is 
also astelic. The astelic stem is then a general characteristic of the 
Equisetaceae, in contrast to the polystelic (gamostelic or dialystelic) stem 
of most Filices and Hydropterideae. 
* Ann. of Bot., v. (1890) pp. 37-62 (2 pis. and 1 fig.). Cf. this Journal, 1890, 
636. t Journ. de Bot. (Morot), iv. (1890) pp. 365-73. 
