y 



The nectary and the sterile stamen of Pentastemon 

 in the group of the Fruticosi A. Gr. 



By 



Prof. Dr. E. Loew, Berlin. 



Ol 



Some years ago I studied in detail the numerous specimens 

 of Pentastemon preserved in the Kgl. Bot. Museum at Berlin, 

 and comparing its flower-structures with those of several living 

 plants of the same genus cultivated in the Botanical Grarden 

 I have now arrived at some new suggestions especially related 

 to the ecology of the nectaries and the staminodium. 



As Delpino^) states, the nectaries of Pentastemon and Chelone 

 are situated at the base of the upper fertile stamens. After my 

 observations in living j^lants of P. laevigatus^ P. campanulatus 

 and other species the nectar-glands are confined to a small cir- 

 cular or elliptical spot on the outside of the staminal base and 

 are composed of a simple epidermical layer of honey secreting 

 cells or glandulär trichoms with hemisphaerical outside-walls and 

 a copious störe of cytoplasm within. There are some species as 

 P. Cusickii., diffusus, gracÜentus, Eattani and others, in which 

 the apex of the glandulär trichoms is divided by 2 or 4 partition- 

 walls as in the head of the stalked glands secreting viscid sub- 

 stances on the calyx, the inflorescence and the foliage in many 

 species of Pentastemon. As intermediate forms are to be ob- 

 served, the glands of the nectary seem to be the descendants of 

 the stalked ones on the vegetative and fioral organs. 



Longitudinal sections of several species viz. P. Menziesii 

 show tliat the hypogynic fleshy honey -clisc of other Scrophulari- 

 aceae has not completely aborted in this case, yet I have never 

 seen freely secreted nectar on it. 



The above described structure and position of the honey- 

 glands on the upper stamens were found nearly in all the species 

 examined by me belonging to the divisions PJiipentastemon and 

 Saccanthera^). Everywhere the same microscopical aspect of the 



1) Ulter. osservaz. P. 1 : 155. 1868—69. 



2) See Asa Gray Synopt. Flora of North America. 2. Part 1 : 259- 

 273. 1878. 



