CELL-DOMINIONS IN THALLOPHYTA 



37 



permanent condition 1 . Thus in Fig. 12, whilst in the axis of first order the 

 whole of the cells are repeatedly divided by longitudinal walls, this process is 

 suppressed in the axes of higher order step by step, and many of them remain 

 as simple cell-rows and appear in relation to the others as formations arrested 

 at different stages of development. We further learn from Fig. 12 that the first 

 branch upon all the lateral shoots is formed on the side next the mother-shoot, 

 and that the first two lateral branches are always upon the same side an arrange- 

 ment which makes it possible for all the lateral shoots to occupy their respective 

 positions without covering one another; occasionally it is true such covering occurs, 

 but if the branches from the beginning were regularly distichous covering would 

 be a necessary result. The lowermost branches are often arrested in their develop- 

 ment; the differences between long shoots and short shoots are therefore here 

 only quantitative not qualitative. 



FlG. 12. Halopteris filicina. End of a long shoot. Seg- 

 ments are cut off from the large apical cell by curved walls 

 and they grow into branches of the first order. These branches 

 repeat the process. The lateral branches of higher order 

 develop successively less strongly. 



FlG. 13. Cladostephus verticillatus. Longi- 

 tudinal section through a long shoot with short 

 shoots. The short shoots have limited growth ; 

 the apical cell of each becomes by division trans- 

 formed into a cell-mass. After Pringsheim. 



Cladostephus, which however cannot be phylogenetically derived from 

 Halopteris, shows a higher differentiation and possesses also a higher anatomical 

 construction. In it we find the following members : 



i. Long shoots. New long shoots arise through a peculiar forking of the apex. 



1 Similar differences occur in the shoot-system of higher plants. In the silver fir, for example, 

 the vegetative points of the different shoot-forms are different. The bud of the chief stem is short 

 and compressed, has a bulky primordium, &c., and is therein distinct from the buds of both the 

 long shoots and the short shoots; buds of short shoots may however be caused to develop as 

 long shoots, and long shoots may become chief shoots. See, with reference to the form of the 

 different vegetative points, Busse, 'Beitrage zur Kenntniss der Morphologic nnd Jahresperiode der 

 Weisstanne, in Flora, Ixxvii (1893), p. 113. 



