ORIGINAL COMMUNICATIONS. 



XVII. — Notes on the Development oe Bulbs and Tubers. 

 By Thilo Irraisch. 



(Concluded from page 124). 



II. TERRESTRIAL ORCHIDS. 

 Spiranthes autumnal is. 



The base of the new tuft of leaves and of the peduncle, which 

 is clothed merely with small adpressed sheaths, is surrounded at 

 the time of flowering with the more or less perfectly preserved 

 remains of the old dry leaves. If these are completely removed, 

 their circular lines of insertion are visible on an extremely short 

 portion of the axis, which holds together the collective parts of the 

 plant. Upon this stands the peduncle, and near this the new 

 tuft of leaves, and at its base the tuberiform roots. 



The number of these is not constant. There are generallv 

 two in the flowering plant, but frequently three or only one are 

 present : the vigour of the peduncle and leaves is in direct pro- 

 portion with their number. Younger specimens which do not yet 

 pro J uce flowers have usually one only: if there are two or three 

 on the same plant, they are for the most part of unequal length, 

 while one is an inch long (a length of two inches is sometimes 

 attained), the other scarcely reaches three quarters of an inch, or 

 even less. But this is not constant, for there is sometimes no 

 difference of size. They are cylindrical and are only slightly 

 attenuated below ; there are generally minute transverse hollows 

 in the surface like wrinkles ; they are thickly clothed with very 

 delicate simple hairs about two lines long, which are very hygro- 

 scopic, curling when dry. The hairs which frequently occur in 

 the upper part of the peduncle are of quite a different construction, 

 for they consist of a simple row of delicate cells, of which the 

 highest is rather the stoutest. There is no reason, therefore, for 

 supposing them identical. At the top of the pseudo-tubers, the 

 hairs either fail or are more sparing. The cuticle sometimes peels 

 off; in which case minute insects have been discovered; whether 

 a new cuticle beset with hairs is in such case reproduced has not 



