16 MR. C. E. JONES ON. THE MORPHOLOGY 
publishing an account of the structure of Lycopodium in his text-book, Sachs (4) made 
observations for himself, and even if he was not the first to recognise the phloem-nature 
of the elements lying between the xylem-bands, he cleared away the idea of cambium- 
layers which is found in previous writings, and further he called attention to the sieve- 
tubes which lie in the centre of the phloem-bands. Two important papers appeared in 
1872, that by Hegelmaier (5), which has already been mentioned, and the account by 
Russow (6) in the ‘Vergleichende Untersuchungen. The former paper is the most 
complete original account of the morphology which has been written, but is confined 
almost entirely to five species; the latter is a brief but pithy summary of the chief facts 
which the author observed in what was presumably a limited examination undertaken 
in the course of extensive comparative investigations. Russow’s account of the structure 
is not altogether accurate; the statement appears (p. 129) that “the phloem (Phloem- 
kórper) surrounds the whole of the xylem and penetrates it by radiating extensions 
whieh fill up the spaces between the xylem-bands"; as he mentions later that the 
protophloems alternate with the protoxylems, and that the differentiation of both phloem 
and xylem proceeds centripetally, it is evident that the “ Phloem-kórper ” includes the 
phloem-sheath, which at that time might have been regarded as part of the phloem. At 
the same time he does not distinguish between them, although he could not fail to have 
seen the well-known iodine reaction; aeain, the numbers which he states for the proto- 
xylems of the species must have been based upon cursory examination. Otherwise he 
presents a remarkably correct account of the structure of the different cells, including 
protoxylems, phloem-elements, and cortex. Hegelmaier’s contribution is not so vigorous 
as that of Russow, but his conclusions have for the most part stood the test of later 
investigations undertaken with improved apparatus. It will be sufficient here to mention 
the chief items which he discusses :—(1) The bilateral character of most of the stems 
and branches which he examined, as shown externally and internally: although the 
arrangement of parallel bands was found to lie approximately in a horizontal position, 
he rejected the idea that this is caused by a force acting vertically ; (2) descriptions 
and figures of the general configurations of the vascular structure and the want of 
proportion between Jeaf-traces and protoxylems ; (3) the structure of the apex, which 
he finds to be devoid of an apical cell, and the methods of differentiation of tissues 
proceeding from the apex; (4) the numbers, arrangement, and development of the 
leaves; (5) the methods of branching ; (6) the formation of the sporangia, and, finally, 
an account of the bulbils of Z. Selago and the mucilage-cavities of L. inundatum. In 
* Die Coniferen und Gnetaceen ’ (7), which was also published in 1872, Strasburger gave 
an account of his examination of the apex of L. Selago, and concluded that in Lycopodium 
there is not a single apical cell as in Ferns, but that a single cell gives rise to periblem 
and dermatogen and one or two cells form the origin of the pler 
of the stem in Lycopodium would be intermediate between the single apical cell on the 
one hand and the three more or less definite meristems on the other. In this paper the 
author also published a description of the bulbils of Z. Selago, which did not agree with 
that given by Hegelmaier, but in the following year, having repeated his observations 
(8), he was able to confirm Hegelmaier' results. In the ‘ Histologische Beiträge’ (10), 
ome, so that the apex 
