322 Sykes. — Anatomy and Histology of Macrocystis pyrifera and 
be interesting in connexion with recent theories of the development of 
connecting-threads k 
The remarkably close resemblance found at every stage between the 
development of the sieve-tubes in the Laminariaceae and Phanerogams 1 2 
would almost have sufficed some years ago to convince us of the truth of 
the homologous theory of alternation of generations, but, though it may 
still be interesting in connexion with that theory, the present knowledge of 
cases of homoplasy is so rapidly accumulating that such a resemblance can 
no longer be regarded as having much weight. 
EXPLANATION OF FIGURES IN PLATES XIX-XXI. 
Illustrating Miss Sykes’s Paper on Macrocystis pyrifera and Laminaria saccharina. 
PLATE XIX. Macrocystis pyrifera. 
The lenses used were Swift’s, Zeiss’, and Watson’s apoc. with six and eight compensating 
oculars. Unless otherwise specified, the preparations were stained by the Safranin method followed 
by London blue. The blue colour in the figures represents callus. 
Fig. i . Cross wall of a cortical cell in surface view, showing arrangement of pits ; note curious 
striations in the wall itself. (Stained watery Methylene blue.) x 600. 
Fig. 2. Cross wall of a cortical cell in surface view, showing the ends of protoplasmic threads as 
dots on the pit-closing membranes, x 600. 
Fig. 3. Longitudinal section of a cell of the inner cortex. Pits are seen in section in the 
end-wall, and connecting-threads traverse the pit-closing membranes both there and in the solitary 
pit (x) found in the lateral wall, x 600. 
Fig. 4. Longitudinal section of part of the lateral wall of an inner cortical cell. An unusual 
case showing several lateral pits quite near together, x 750. 
Fig. 5. Surface view of a very young sieve-plate, from the outermost row of secondary sieve-tubes 
in an old stem. The ends of the threads are seen as fine dots and are arranged singly except on the 
periphery of the plate, where a few groups are seen, x 600. 
Fig. 6. Surface view of a slightly older sieve-plate, being the second element in a radial row, 
counting from the outer edge. The threads are arranged throughout in groups of four, five, and six. 
(Stained Safranin and Acid violet.) x 600. 
Fig. 7. Surface view of a sieve-plate, showing progressive differentiation from the centre to the 
periphery. A mass of deeply staining protoplasm hides the centre of the plate, where probably only 
single threads would have been found. A few single threads are still visible round this mass, but 
most of them have each given rise to groups of two and three threads. Nearer the outside, groups of 
five are present, and those represented as surrounded by a ring have already developed callus, while 
on the extreme periphery single slime-strings, each formed from one of these groups and enclosed 
each in a single callus-rod, are found, x 600. 
Fig. 8. Surface view of part of a sieve-plate; a slightly older stage than Fig. 7, with callus 
represented blue. In the centre are seen groups of threads (a) which have not yet developed callus 
Around these are groups of more deeply staining threads each enclosed in a callus-spot (3) ; nearer 
the outside the callus-spots forming a group have united by their edges to produce a ring ( c ) ; 
d is a case in which the threads, callus, and portion of wall enclosed by such a ring have begun to 
break down, and have given rise to two slime-strings; on the periphery the process of boring out is 
complete and a single slime-string {c ) has been produced from each original group and is sur- 
rounded by a thick ring of callus. In one place (f) the callus has begun to spread over the portions 
of the wall which lie between the perforations, x 600. 
1 Gardiner, Roy. Soc. Proc., 1900. See also Meyer, A., Die Plasmaverbindungen und die 
Fusionen der Pilze der Florideenreihe, Bot. Zeit., 1902, p. 139. 
2 LI ill, 1. c. , 1901 and 1903. 
