DEVELOPMENT OF SIUM CICUTAEFOLIUM. 5 



would scarcely be suspected. I am not aware that this seedling has ever 

 been described, and the striking- variations in the form of the juvenile 

 leaves make description difficult. 



The cotyledons are quite similar to those of many other of the Um- 

 belliferae, being narrowly oblong or elliptic oblong, rather acutely 

 rounded at the apex, and tapering gradually into a petiole at the base. 

 The petiole and blade together are 1.5 to 2 cm. long and the blade is 

 2.5 to 4 mm. wide. 



The early " nepionic " leaves are extremely variable, but it is rare 

 that they do not consist of a single blade constructed on a somewhat 

 palmate plan. The blade is usually of rounded form and quite variously 

 notched, cut, or lobed. In order to facilitate a systematic investigation 

 of the variation in these leaves they were divided into several more or 

 less artificial groups. The first nepionic leaf in more than 120 unse- 

 lected individuals* presented forms which were placed in six of these 

 categories, as follows : 



(a) About 10.5 per cent were divided palmately into five nearly equal 

 lobes, one or two of which were sometimes slightly notched. 



(b) Twenty per cent were 3-lobed, with the middle lobe 2-notched 

 and the lateral lobes each bifid. 



(c) The leaves in the third group were likewise 3-lobed, but the lobes 

 were quite variously notched. Over 28 per cent of the seedlings had 

 the first leaf of this description. 



It will be noted that the form of leaf described under (b) is simply a 

 special case of (c), and was separated from it because this was the only 

 form of trilobed leaf which could be so definitely characterized, and 

 because this simple definite type of trilobation is almost wholly limited 

 to the first nepionic leaf. 



(d) Over 15 per cent showed the tendency to trilobation by a single 

 cleft on one side, unmatched by a cleft on the opposite side. These 

 will be spoken of as " half 3-lobed leaves." They pass gradually into 

 a form having one lateral leaflet, and these two conditions were kept 

 together in a single category. 



(e) Nearly 25 per cent had a generally rounded, ovate or cordate 

 form, merely dentate, or irregularly cleft in a manner which did not 

 suggest trilobation. 



*The seedlings were taken up on two small clumps of earth from their native 

 (habitat near Robej'-, south of Chicago, Illinois. The individual seedlings were 

 carefully separated and all were transplanted about 3 cm. apart in a regular pat- 

 tern in glass dishes. The point of departure for each dish was marked and a 

 number assigned to each seedling, so that drawings made from time to time could 

 be labeled in a manner to allow .the progress of each individual to be followed. 



