846 Mr Macvicar on the Seed of the Stipa Pennata. 



envelopes it. Thus the strong outer covering of the seed is pro- 

 duced below into a very sharp rigid spine ; and terminated above 

 by a long awn, which is articulated to its summit. Originating 

 near the base, and proceeding up certain ridges on this the invest- 

 ing valve chiefly, are lines of stiff hairs pointing upwards. The 

 awn, when fully developed, is about thirty times the length of the 

 seed, or about fourteen inches. It is round, tapering and plumose, 

 with the exception of about three inches at the base, which are 

 compressed, longitudinally sulcated, and without hairs. 



The seed, therefore, and its appendages, possess a structure 

 such as is imitated in a barbed and feathered arrow, which is so 

 well calculated to find its way into the ground in a vertical di- 

 rection. Many seeds, however, possess a similar structure, and 

 it is not this which gives to the awn of the stipa its most striking 

 peculiarity. It is a change which takes place upon the awn, 

 after it has left the plant that produced it. When it has fallen 

 from the parent plant, it enters the soil vertically, and in a few 

 hours the base and sulcated part of the awn becomes twisted, 

 and the feathered portion becomes horizontal. In consequence 

 of which, it is blown round by the autumn winds like a vane, 

 and every turn screws it farther down into the earth ; for the 

 hollows and ridges which, when it remained upon the plant, were 

 only longitudinal sulci, have now given rise to the hollows and ele- 

 vations, in a word, to the threads of a screw. Thus it is rfioved 

 down, and whatever is gained, is prevented from being undone 

 by a reverse motion of the vane, in consequence of the stiff hairs 

 upon the glume which act as barbs. 



When it has been thus worked down into the moist soil, into 

 the situation most favourable for germinating, the attachment be- 

 tween the awn and seed is dissolved ; for having drawn up many 

 when they were in this condition, I have invariably procured the 

 awn only, and never, by any chance, the seed. Such appears to be 

 the function of the " spiral articulated deciduous awn '' of this 

 interesting species *. 



• The seeds of the Stipae often occasion great inconvenience and trouble 

 to travellers, and even to the domestic cattle of the districts where they grow. 



This fact is well stated in the following notice by Mr Raspail Ed. 



" On the morbid accidents to which animals are exposed by the seeds of Stipa pen- 

 nata and capiUala.-^lt is known that the husks of the genus Stipa terminate 



