xix] 



HABIT 



45 



highly variable within the genus. In the smallest forms both parts may be 

 unbranched, as in B. simplex (Fig. 336, a-d): but the commonest condition 

 is that where the sterile blade is simply pinnate, and the spike the same, 

 or more highly branched, as 

 it is sometimes in B. Luuaria 

 (Fig. 337). In other species 

 of larger size the sterile blade 

 may be three or four times 

 pinnate, and the fertile spike 

 shows corresponding com- 

 plexity, as in B. daiicifoliuin 

 or virginianuvi. The genus 

 as a whole shows such gentle 

 gradations of change from 

 the simplest to the most 

 elaborate that the unity of 

 type is unmistakable. Various 

 abnormal modificationsofthe 

 leaf have been described for 

 BotrycJiiiivi involving the for- 

 mation of accessory parts, 

 such as doubling of the sterile 

 blade, or increase in number 

 of the fertile spikes: but no 

 species is recognised in which 

 these changes have become 

 permanent. Abnormalities 

 involving the distribution of 

 the sporangia are the most 

 important. All stages of the 

 vegetative development of 

 the fertile region have been 

 found, even leading to the 

 complete replacement of the 

 sporangia by a structure like 

 the normal sterile blade. But 

 on the other hand it is not 

 an uncommon thing for spo- 

 rangia to appear upon the Fig. 337. Botrychittm Luuaria Sw. a, forma normalis 

 ., - f 4-1 1 r Roeper; b, var. incisa Milde; c, var. sitbincisa Roeper. 



Sterne region 01 tne leat (^^ natural size.) d, part of the fertile spike, with open 

 (Fig. ^38). Moreover not a sporangia, enlarged, e, two open sporangia somewhat 



bent asunder to show their attachment, enlarged. From 

 part only, but even the whole Luerssen, in Rab. Krypt. Flora. 



